I have used one of these trucks for over 15 years with no major complaints except lack of horsepower for what I was doing. I had an 11 foot plow on it for winter, a 32 foot flat bed trailer for hauling farm equipment, and used it to haul grain and stone. I put a hoist under the bed. It was not abused and was not babied.
I never had any transmission failures. I followed my tranny shop guy's advice and got the engine oil out of it and put in Dexron. He used to work on them in the military, then built the GM equivalent of them out of cars in civilian life for racing, and said the engine oil was the biggest problem. I also periodically removed the front cover on the trans pan and cleaned out the water/oil cooler where crud can collect and inhibit cooling. I also kept the bands adjusted, especially the level of the indicator pin on the side of the tranny valve body boss.
I was not afraid to use high reverse, I just used my head and listened to what my truck was telling me when I did. As was said in another post, using high reverse when heavily loaded was many times not possible unless on a hard level surface. I would ease into the gas, giving the truck time to get moving. If it resisted moving, I would then go to low reverse. I liked the idea of Memphis Equip's Reb Shifter, but did not buy one because I would have lost high reverse. I would not have liked having to back out of the blind alleys I plowed in low reverse. I also used high reverse many other times like backing to the dump point at the elevator and backing down long drives to dump stone. Just be an operator in tune with your truck, maintain it well, and it will serve you well.
In my experience, the tranny is not the bomb waiting to go off it has been many times portrayed to be when properly treated.
Regards Marti
Do you mind me asking what he is asking for it? 
Alot of tec. help here....Everybody loves the old GMC`s hehe
