1989 srv issue

Hey there. I have 3 srv's, my 1989 is really making me scratch my head. It ran great last year. This year it's got a weird hesitation and little power at about 15-25mph. It ideal great and will take off like a bat outta hell but doesn't run good at low range. I have the tors bypassed, ground wire from frame to motor, cleaned carb (pilot was clogged I thought that was it but it wasn't), bypassed all electrical components includinf lights and switches, switched external coils, new plugs, cleaned carb twice and it was very very clean. Now if I have the sled off the ground when I rev it up it's perfect, you would never know the it has an issue. When riding on it under load it acts up. Seems to me that's it's using a little more gas than usual too but not sure on that. Like I said starts right up idles great but just can't get this figured out. Please let me know if you think you have an answer to help me. Starting to think fuel pump!? Thank you all

1989 srv issue