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Seeking some advice - 1990 K3500 6.2HD Utility truck

1397 Views 27 Replies 7 Participants Last post by  benthecomputerguy93
New guy, first post. If this thread is in the wrong subforum then I apologize. Also if I happen to leave out anything important here then please let me know and I will add it.

Starting at the beginning - I recently purchased a 1990 K3500 with 40k original miles. As I understand it, this truck was originally a special order for the fire dept. in a small town around here, but they ended up not using it, so it was then sold/sent to the water dept. in that same town where it was then used for 25 years (thus the super low miles). The first thing I did after purchasing was take it by a local shop where I get some work done, and have one of their guys look it over. This individual co-owned a chevy dealership for about 30 years so I figured he would be able to tell me more about what I had. His answer surprised me a little, and that's why I'm here. He claims to have never seen this exact configuration before, which could have something to do with it being a fire dept special.

Here's what we have:
  • 4x4 but its a split diff with a skid plate (according to him, it should normally have had a solid axle)
  • 16" 8-lug wheels (he believes that stocks would have been 19")
  • 159.5 wheelbase - (this is where he explained to me the difference between a cab+chassis configuration, versus a simple "bed delete" option on a normal truck, with the different frame-rail spacing, axle width, etc. He was a little bit perplexed because he couldn't tell which one it actually was. Also said he thought this length was common for a crew cab, but not a single cab)
  • He ended with saying that because this was the body-style change year for the 3500, this was the first year of these and it could be some one-off deal due to that.
I realize that this guy could just be old and confused. He could also simply be full of crap. Thats why I'm here.

So what do I want? Two main questions, at least for now.
  • I bought this not realizing it might be "special", just hoping to adapt it to pull a camper. I'm curious if there is even anything I can easily fit on the back, to replace the utility bed that is there currently, since thats not really convenient for my intended purpose. I have no idea where to look for such information, and even if I did, I'm willing to bet that without knowing exactly what I have, it would lead to some pretty confusing results. I thought about trying to fit a 8' regular bed on it, but then that leaves a ~3-foot gap between the bed and cab. I've seen this configuration a time or two, with some sort of frame-mount basket or something fitted in between to take up the space so it doesn't look stupid. Any advice or suggestions, first-hand experiences are much appreciated.
  • Whats the deal with this engine? I've read some pretty mixed things about the 6.2HD, but most say that its made more for economy than for pulling, even though this is a 1-ton truck. If this is the case, then I may be better off trading it off for a cummins or something. Again, any advice is appreciated.
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Alright I'll get some more pics and post back later today!

As far as the engine, thats probably right for the power, I'm just worried about having to start climbing hills a half mile before the hill...if you know what I mean. I've read where many say that it will indeed pull anything but you'll lose 20mph on the slightest grade.
No 2-speed rear end that I'm aware of. Guess I should look around just to be sure, but I haven't noticed a shifter for that. And I guess the 3-speed trans is why it always feels like there's no overdrive....because there isn't haha. I thought I had a 4L80E with OD. Whoops. That makes me wonder how difficult it would be to do a swap on that rear end though.

We do not have a camper yet.... My wife and I are looking to get something in the neighborhood of 30-feet. Not sure if we want bumper-pull or fifth wheel. I'm sure I can find something heavy to pull around though... *looks around at the vehicle graveyard*
Beach, the M40 is his transmission code, a manual 3 speed

No overdrive in the transmission, so the 65 mph revs will be kind of high
Wait. I didn't catch this yesterday. This truck is an automatic, and there is no hole in the floor to suggest that it ever was a manual, unless they did a really good professional swap. I suppose I could check it out from the underside. So I wonder what transmission I have then?
look into a turbo
Thanks for the tip. Yeah, I doubt my wife would be too keen about a soot-covered camper... What are my options for adding a turbo? Pros/cons? Cost...

My bad!!!!

The M40 is a 3 speed automatic, the Turbo 400

Sorry Ben and Beach, must have had too much rum when I checked that code.
Haha, quite alright. Good to know its something pretty common.

So with the TH400 and 4.10 gears, you can pull anything you want, but you won't be going over 65 mph (unless you want to get 1 mile per gallon.
Right... So what are my options for changing this?

Thanks a million guys, you have all been extremely helpful so far!
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Good points all around. I'm not opposed to selling it and for what I paid, I could probably turn a slight profit. The guy I got it from said that in the ~24 hours he had it listed (facebook) that he had 28 people contact him about it, so there is definitely interest around here. That option is starting to sound more appealing because then I could turn around and look for something more suited, and have some money in hand if I find something. I had originally wanted a 4x4 diesel suburban actually...

Well, let's try to figure it out, we know the rear ratio, the trans gears, all we need is tires.

Ben, could we have the rear tire size?
And then you write this after I had all that up there typed haha. I'll check it out in a bit.
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Well, let's try to figure it out, we know the rear ratio, the trans gears, all we need is tires.

Ben, could we have the rear tire size?
235/85 R16
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