Tranmission Problem...I think!

I own a 1998 GMC Jimmy. It has 130 000KM on it. The person i bought it from never serviced the tranmission in any way including not ever changing the transmission fluid.
A couple of days ago while slowing down for a traffic light, my ABS light came on. After stopping at the light, the Jimmy would not shift out of first gear (it is an automatic transmission). The RPM's would rise but it would not shift into second. Then i punched the gas hard and it shifted. But it didnt shift into second...it shifted right into third ( i found out later as i increased my speed). I got it home and let it sit all night. It was fine in the morning for about 20 min of driving and then i had the same problem. I have had the transmission fluid flushed and filled and have added special treatments to the transmission oil. Sometimes just hte ABS light comes on and other times both the ABS and the CHECK ENGINE light come on. I have a feeling that this problem occurs only when the tranmission temperature is quite hot. Anyone have any ideas to whats going on. I just hope the solution doesnt involve replacing the transmission itself cause i dont have that much money right now. Thanks!

You are correct thinking the problem is tranny related. These trucks have defective valvebodies that have problems after getting some miles on them. I have seen the problem many times and is easily fixed by installing a new revised valvebody. Your check engine light is coming on because it is detecting transmission slippage from the hard or inaccurate shifts. If the trans has 130,000 miles on it and is original there is a good chance its whooped and should probably be over hauled anyway, but if your just looking to get the issue fixed replace the valve body and I'll bet it fixed. I got my valvebody from Trans Star in Philly Pa because they are a dealer for Valvebodies Express that makes the valvebodies with all the updated parts and revisions done already. If you really wanna be cheap you can just buy the repair kit and attempt to fix the one you got but I don't recommened it. Expect to spend around 300 bucks for the valve body Good Luck

The threadstarter's problems are not the typical symptoms of a worn valvebody. The weakness of the valve body is in the TCC lock-up. When the tranny detects a slip from the TCC apply, it commands max line pressure which causes a hard 1 -2 shift. After detecting the slip twice, it sets DTC P1870.

In the threadstarter's case it appears that the tranny fails to shift to the proper gears. Due to the ABS and Check engine light illuminating when the problem occurs, I'd say that the VSS or the VSS circuit is the most likely suspect. Retrieving the stored codes will help diagnose the problem.