Uneven power when starting and from 35-45mph

[VTXorcist]

Hi all, I just bought a used GZ. I knew from the get-go that it had a crack in the exhaust, just before the megaphone where the pipes converge. I bought a new-to-me exhaust (used off ebay) and I'm waiting for it to come in.

My problems are two-fold and may or may not be related. I sometimes lose power in 1st and 2nd gears (occurs even after the bike warms up). The bike starts moving then putters out no matter how much twist I give the throttle. If I lay off a bit, I can usually keep it from stalling and eventually coax it up to where I can shift to 3rd. It's intermittent; some of the time I can twist and the little engine roars in 1st and 2nd, no problem.

Also, around 35mph up until 45mph, if I cruise in 3rd or 4th, I get really uneven power. The speed stays relatively constant, but I can feel the bike jerking under me. Below 35mph, it will cruise contentedly in 3rd or 4th. Above 45mph, it gets happy and cruises without complaint in 4th or 5th.

I was thinking maybe the exhaust had something to do with it, so I'm waiting for the new pipe and hoping it will fix the problem. In the meantime, has anyone experienced these problems and do you have any recommendations for diagnosis and fixes?

Thanks!