I own a 82 3/4ton chevy with a 454 4speed stick 9"of lift and 38.5x14.5 tires its frame is rotted on the front mount of the rear leaf spring. If i take truck to a good welder can he weld in a new section of frame and make it sturdy enough to take moderate off roading?and How?  

As long as it's a certified welder it should be no problem. Check the bottom of the spring mounts, there is an opening that's supposed to let water drain out, but they often get clogged up with mud and will rot the frame out in a hurry (as you found out).  

Depending upon the extent of the rot and how much your willing to spend....You might look into a frame replacement from a bit in front of the rot to the back end.  Not really necesary but it will make for only one weld instead of splicing a piece in.  Either way can be done just as strong as the other but I would still have more confidence in the single welded up piece, if done properly.

MM

thanks for the info