Ok, I've tried searching the threads and internet trying to figure out what transmission could be in my1988, K1500 Silverado, standard cab, long bed. I was told by the previous owner that a heavy duty diesel transmission was put in it so the numbers in the glove box don't do me any good since the truck has always been powered by a gas motor. I got underneath the truck and pulled these numbers: 15694903GAKH 1500 C 02 1795 Castrol syntoro LT GM P/N 12346190 Chrysler P/N 4637570 The last three lines pertain to the transmission fluid and I've searched using the numbers/letters in the first line but nothing gets it. The closest I've found is 15691903GAKH...The 1 is the difference. I double checked the tag on the transmission to make sure I didn't misread it, and it's correct. And the site I found says it's on a 2wd, mine is a 4wd. It looks similar to the NV4500, with only minor differences in the main body of the transmission. I'm not sure if those are the differences in the heavy duty versus the medium duty. 1st gear is a granny gear, and the rest are normal. The reason I'm trying to figure it out is because the synchronization gear going into 3rd is bad and I want to replace it. Basically like shifting without the clutch, I have to find the sweet spot before it will go in. Any thoughts, websites or knowledge to share??:neutral: Thank you in advance!