I have a 1991 GMC K2500 long-wheel-base 5.7 V8. I was just having some tranny problems, which I think I have fixed, and it got me to thinking. If for some reason I have more problems and I choose to just get a used transmission, which one would be best. It has a THM 700r4 in it but if I could get a good price on the 400/3L80, would that be a good/bad choice. I guess my question is: what are the pros and cons of each one, the THM 700R4/4L60 and the THM 400/3L80? Let the games begin. PS: Will a 4L60E work in my truck? I was just wondering. Thanks.