problems with my tranny

I know that before I was talking about how to lift my 78' 3/4 ton but now there are bigger issues. This has been happening for a while, but things seem to have gotten worse in a hurry. Being the 2nd 727, and sitting in the dirt for 10 years until I started resoreing it, I think it has done remarkably. I have just put over 4000 miles on the rygg since I redid the engine and 600 was towing a old chev on the freeway just last weekend. Things started to get worse after that trip. It always had a little slip from one to two but now its pretty bad. She needs some help! I was thinking of a complete rebuild kit but then adding a transgo tf-2 shift kit. I have always wanted to control the shifting from somewhere other then the colum so I have been looking at the B&M megashifter with the TF-3 kit. Has anybody heard of this combination? Interested to know anything. I want it to be fun driving but also fairly easy. Is this possible? Thanks, Brooks