When you replaced the slides - did you loosen the track a little to compensate for the extra thickness on the new slides (compared to the old, worn ones)? Maybe it's too tight?
Here's a couple of things to do:
- Remove the drive belt
- Put the rear of the sled up in the air
- Turn the secondary / driven clutch by hand to get a sense of how it "feels"
- Loosen the jam nuts on the adjuster bolts at the back of the track
- Loosen the adjuster bolts, paying attention to count how many turns you move each one
- Place a 2x4 or similar sideways across the track, "behind" the two idler wheels that move to control track tension and tap with a hammer to push them forward
- Once you have the track fairly loose, reach up into the front of the tunnel on each side and see if you're able to move the driveshaft in any direction (up, down, side-to-side, etc). If it moves, other than rotationally, you likely have a bearing issue.
- Visually inspect the drive cogs to ensure they are not worn and are able to properly engage the track
- Find an object that weighs about 10lbs and will fit between the rails of the skid - place this in the middle of the skid to push down on the track
- Start to tighten the track, paying attention to how far down that weight pushes the track. You want 1" to 1.5" of 'droop' in the track from that weight when it's tensioned properly. You could throw the weight in there before you start to see how well it's currently adjusted.
- Spin the track by hand (remove the weight, spin, replace the weight) a few times to ensure that you're getting the sag all at the bottom of the skid.
- Once you have the tension set correctly, and you're sure the track is straight, tighten the jam nuts and remove the weight from inside the skid.
- Loosen the jam nut on the chain tensioner
- Unscrew the chain tensioner a turn or two, then turn it back in by hand as far as you can
- Unscrew the tensioner 1/4 turn, hold in place, and re-tighten the jam nut
Turn the secondary by hand again at this point and decide if it feels any smoother than before.