Sorry for the long post but here it goes... I have a stock 96 impala with 142,000 miles on it. I've had the car since 2003 (It had 81,000 on it when I bought it) and it has been my daily driver up until last year when I bought another car to drive back and forth from work. Transmission fluid has not been changed since Ive had it and I dont know when or if ever the previous owner changed it or not. The car has been sitting for about six or seven month now. So I decide to take it out for a spin and noticed it seemed to be slow in shifting when I first put it in drive and give it gas (the 1-2 shift?). The car runs fine below 55mph and above 55mph. But if I stay at 55 mph, the car seems to be having a miss or something. It feels kinda like its jerking. RPM's are not bouncing around. So I put it on cruise control at that speed and again the jerking around starts and the check engine light came on. I hook it up to the code reader at Autozone and get p1870. Is it shifting in and out of OD? I have read the stickey's and all and from what I gather maybe a transgo is in order? I am not much of a mechanic. The biggest fix I have ever done to the car is replace the radiator. What do you guys think it is? Thanks for your help and once again sorry for the long post.