Something very wrong..help?

[69-Chevy-350]

I took the old girl to dump some trash..two barrels..nothing heavy and then over to pick up fire wood. On the way to pick up the wood, it was like there was something breaking or falling apart. I pulled over and in nutreul the truck was fine no noise. But when I started sriving I had lost power. When I hit the gas the engine rpm goes up but I can't get any power to go anywhere. Light touches of the gas and she would move but anything more then very light and it just revved. I also smelled some kind burn smell.
If it helps I have a 350 (replacement) and a 3 speed on the floor. Their is basically no gear box as you kind of just through it in the gear you want to go and have faith that it is in right. I was also having difficulty shifting it in gear before this all happened. It was the first time I had problems. I was thinking either the shifter is bad or maybe the tranny is no good. There is a pretty bad leak from the speedometer cable. Any help here guys would be of great help. Sorry this runs so long. I still can't get my digital camera working otherwise I would have pics. Thanks for the help again.