shifting problems

I have a 2015 GMC Sierra HD 3500 Denali diesel that will not maintain RPM nor shift from 4th to 3rd gear when towing a heavy load up hills. Speed will decrease until about 40 mph before it will shift. I've had similiar GMC trucks for 18 years, towing basically the same type of load. Never had...

Our transmission is having problems in reverse (meaning it will not go into reverse). When in reverse it feels like the vehicle bogs down. As well as in drive will not upshift into second nor any other gears. I have the v6 vortec style engine. I have some basic understanding to rebuild this...

Heeeeelllpp!!! I purchased a 95 GMC pickup about a year ago. It had sat for approximately 3 years. The guy I bought it from said the 305ci motor had been rebuilt before the 4L60e transmission went out and they didn't want to put anymore money in it. So they parked it. The transmission would go...