Transmission

I just replaced my transmission in my 1999 Mazda B3000 yesterday 12/10/15. Drove it out of my garage and drove it around the block. Was driving great, shifting perfectly, then I came to a stop sign and put it in reverse and then back into drive and it seemed to have lost a lot of power and just sluggish and shuttering. Continued to drive back to my house and on came a horrible burning smell and I popped the hood and it was smoking. I looked under my truck maybe for a leak and there was none. Do you have any clue what this could be?