He did say that it starts to act up after he has driven down the highway and then exits and catches a red light and then from there it shifts hard.

 

i think there may be a bullitin for that year tranny. don't quote me on it though. but if there is then theres a new valve body available that might fix the problem. if not an 1870 usually means the tranny is toast.

 

96 there was a PCM ground problem,so your buddys ok there being a 97, typical trans slip code,If he didnt run it long like this and hasn't heated the converter,he maybe able to get by with pulling the valvebody and do a repair, the cheap way is with a single (finding the correct one is the key)next would be installing the JR. $35 trans go kit,Most folks go for the sonnax reamer and replace the TCC valve.What happens is the TCC valve bore wears and slippage is seen by the PCM and it goes into limp mode which then make full line pressure hence hard shifts.

 

Interesting.