sluggish transmissin rtv900

I'm new and i must confess i just joined because i just picked up a rtv900 with a trans issue. when you first start it and put it in gear and try to go it just free revs. if you hold the throttle down it will finally take off and go but has very little pulling power. it still just about throws you through the windshield when you stop so I'm thinking the swash plates are ok. also the pump makes a lot of noise when it finally takes off and the fluid on the dipstick is really foamy. the filters and fluid have very few hours on them. where should i start before i pull it out and replace the pump. thanks for the help in advance

sluggish transmissin rtv900