belmead

Hey there I just bought a 99 banshee. its basically stock except for pipes and jets. When I get on a straight run the acceleration is very slow, and when I get to 6th gear it loses revs and starts to slow down drastically. I can go faster in 4th than 6th Some times the throttle lags as well and almost stalls out the quad in 1st. Ive had it at a shop and they adjusted the mid range needles and checked the compression. The shop tells me nothing is wrong with the quad but clearly there is. The throttle cable has some appoxy on it as a quick fix from the owner before me. Any ideas what could be wrong with it? Should I replace the throttle cbale assy? Could it be the clutch or the gears? Thanks in advance!!