I Have A Problem And Need Help!!!!

i know this is in the wrong forum but i posted it in the gmc forum and nobody answers, i figured since there is more people reading nissan forums ill give it a shot
I have a 1995 Gmc Suburban c1500, automatic 2wd. I've been having transmissions problems for some while. the trans. works good in a everyday drive, but when we go on trips i have problems. It starts out well but after a couple of hours of driving it starts to fail. The speed goes down and when you accelerate it doesn't. It just makes a sound like your reving it but no speed. It goes up to 25 mph and doesn't want to go up. i need some advice please help.

This is an easy one....if you have about 60,000 to 80,000 miles on the odometer, your reverse/direct drive clutch pack is worn out. Eventually your truck won't even move from a dead stop. Smell the ATF. Does it have a burnt smell? Is the ATF red or a burnt brown? That confirms it. If the ATF doesn't smell burnt and still has that red ATF look, look under the vehicle for a vacuum line to the transmission. Is that vacuum line in good condition or could it be leaking? Also check the vacuum line connection at the engine. That vacuum line affects the shifting. If that line looks rotted, replace it with a better quality line such as a fuel hose of the same size. (*I'm about 75% sure that the information I just gave you applies to your vehicle)