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hey guys i have 99 chevy crew cab with a 454 and 4x4. recently i have noticed some slipping while in over drive at 70-80 ish not real bad but it has me worried. tomarrow im changing the fluid and filter to see if that helps but if it doesn't i would like to put in a 5 speed since the automatic is the only thing i dont like about the truck. i just have a few questions about the conversion i know i will have to be adding the clutch peddle but that should be pretty strait forward if i just remove the parts from one from a junk yard right? and i have herd that i can get a 5 speed from a sb chevy and change the bell housing with mine it will work but i dont like the sound of that. it has 35s on it so i dont want a weak tranny any suggestions guys
 

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I believe you will need to change the PCM and parts/all of the wiring harness.
 

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The 4L80 is a very strong transmission, hard to go wrong with one.

The slipping is most likely the torque converter. The "clutch" material can wear loosening lockup strength. The slipping can worsen as it gets hot. A couple of relatively simply things you can do to improve TC performance is to replace both TC solenoids. A Superior shift improver is also an excellent upgrade, but a little more work.

When you do your fluid/filter change it's good to pump out the old fluid. I simply remove a transmission cooler line to do this. The process has been outlined on this site dozens of times. When you put the fluid in, add some Lube Gard. You want the red bottle with red cap. It's an excellent product, and everyone here should be running it.

http://www.lubegard.com/C-112/LUBEGARD+Automatic+Transmission+Fluid+Protectant

In the super easy yet surprisingly effective products, try adding some Dr. Tranny.

http://www.lubegard.com/~/C-230/Dr.+Tranny+Instant+Shudder+Fixx

I had some TC shudder in my Tahoe. This stuff instantly fixed it, as advertised.
 
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