I just had my valves adjusted and had the shop install a full system yoshimira exhaust i got my 2000 gsxr 750 back today and it wont rev past 5000 rpm. the guys at the shop told me i should buy a power commander and it would fix the problem. they said it was running really lean becaus of the exhaust and k & n air filter. are these guys trying to pull my chain or wut?