I few years ago I had my 700R4 rebuilt, and ever since it will not stay in lock up when I am just cruising down the road, I have only put about 300 miles on it since then and weather I'm doing 40 or 70 on a flat surface its always seems to down shift out of OD and I have to step on the gas again to make it go back into lock up only to have it come out again. I took it to another tranny shop to have it looked at and they told me everything is fine inside, but the shift kit its has installed is to radical and is causing the tranny to act that way. Just wanted some feed back to see if you'll can tell me if they are right or not. They quoted me around $500.00 to take that shift kit out and replace it with a milder one. My rig is a 1990 K5 with 5.7 liter, 4 inch lift with 33 inch BFG's and running 4.10 ring and pinion. Thanks for any input.

Respectfully

 

Sounds legit from what they said,but 500 bucks. damn. take like 2 hours max to change it,and the shift kits are like 50 bucks. id check elsewhere. 60 bucks a hour usually around here, plus fluid and kit shouldnt be more then 250 bucks max.

 

Thank you for you help, would you happen to recommend a good shift kit or do you think I should just do a lock up kit. I'll definitely look around for another place. I only took it to this place first because they didn't charge to check her out.

 

Which shift kit are you running? It may just be the tcc lockup sensor going bad. here is one here
4L60E 700R4 TCC Solenoid 1982 1993 | eBay

As well as the tv cable being out of adjustment. it controls line pressure,shift points etc. read this :
700R4 Throttle Valve Cable Adjustment

good luck.