I have a 97 K1500 with a 4L60E that is not shifting right. i have 1rst,2nd, and reverse but when i put it and drive it seems like ti wants to down shift. if i put it in 1rst and than shift into second its fine but when i shift into third is when it starts having problems. would that be the shift sensor going bad? or some thing else. I have head this a common problem with these trannys.

 

are you saying it feels like it goes to neutral or really its back to 1st which gives a neutral fee? If so your 3-4 clutch pack has failed .

 

It doesnt shift right in drive but shifts normal manually from first to second but doesnt want to shift into third

 

I agree with Performabuilt, sounds like the 3-4's are fried.