GMC Repair: 88 gmc 1500 bad vibration and high gear take offs, technical service bulletins, service garages

Question
I have a 88 gmc 1500 with a 5.0 and 700r4 I have had some vibration problems and shift problems .not all the time .there are times you try to take off from a light and it is like you are taking off in high gear. The check engine light was coming on at times and the codes showed a bad ecm it was changed it seems to run a little better but still haveing the other problems any help would be helpfull. thank you  ps all the mounts and drive lines all have been checked and also a new torq converter installed  

Answer
Hi Rick. I believe what you are experiancing is called a safe mode in the transmission, I'll explain. The transmission you have has shift solenoids in it, If there is a problem with the transmission or the solenoids, the ecm will put the transmission into second gear and lock it there so as not cause damage such as if the transmission is in 2 gears at the same time, hence the title, SAFE MODE. This should be checked by a qualified transmission technician. You may only need a new shif solenoid. As  for the vibration, were the U joints checked closely when the drive shaft was out ?  Have your local dealer check to see if there are any technical service bulletins for this problem, or, most service garages also have this information if they are up to date with their equipment. Please let me know what the problem was should you get it fixed so that i may put that into my data bank to help others with the same problem. Please get back to me if you don't have any luck and I will work with you on this further.MANFRED