1995 Chevy 3500 HD 6.5L. The transmission won't shift out of low gear. When the dealer hooks up his computer he can make it shift using that. Is there a computer made that I can purchase that will shift the transmission electronically? Have you ever heard of a problem like this before? The dealer also said it could be a very simple problem (maybe a short), but he would have to do a ton of work to locate the problem and resolve it. Please let me know if you can help. Thanks,
Ryan

If he can shift it with the Tech 1 then it sounds like there is an input missing to the TCM, most likely a speed sensor. Ground the 2 top right terminals on the data link connector together, turn on the ignition and count the blink codes. That should point to the electrical problem.