Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

I have a Toro 824XL Power Throw, 8 hp tecumseh, 5 forward & 2 reverse speeds,  it runs fine , but when I put it in 1st gear and depress the drive handle it goes backwards, very slowly, the same thing occurs in 2nd & 3rd gear. It will start to go forward when in 4th & 5th gear, reverse 1 & 2 seem to work fine ?? Any sugestions, could it be the drive belt? 

 Thanks Biffr1