Drive Belt Adjustment

So I just picked up a 1978 Bolens G11xl the other day and have resolved all its little gremlins but one. It runs great and will drive but is most responsive in 1st and Reverse. It will go in other gears but its a struggle. It shifts very smooth and doesn't grind at all. I dropped the mower deck and climbed underneath. It has a shaft coming directly off of the flywheel side of the engine that connects to what must be a worm drive with a pulley for the drive belt. The drive belt rides on three pulleys, one on the worm drive, a second on the transmission and third on a tensioner pulley. When I operate the clutch/brake pedal I can see the tensioner pulley move back and forth to give and take slack away from the belt but it appears to be pretty loose in either position. When in gear I can smell burning rubber telling me that belt is slipping but I cant figure out how to adjust it. There was two rods coming from the back by the transmission and connecting at the clutch/brake pedal. Both were threaded on the end and one had two adjustment nuts on it. When I adjusted it all it did was reduce travel of the pedal and the other rod seems to be stuck in its current position with the adjustment nut being about an inch away from the point of contact between the rod and clutch/brake. The nut appears only to prevent it from falling off and I'm not sure that any adjustment of it would matter anyways. If I'm missing something please let me know.