well, we know its not bad gas. you just did the tank, yes?
thats a tough one. check everything. does it ONLY do it when your moving? and only in that rpm range? if so, i have put driveshafts in without centering the rear ujoint, and had similar vibrations. since you recently had your tranny out, that would be something to check. normally clutch problems will chatter while releasing the pedal, or just slip. see if you can get it to do this while standing still, under load. this will help you determine if its engine only, or drivetrain connected. i have even gone so far as to put a car on jackstands and simulate driving to chase down vibrations. sometimes even keeping the p. brake on for short periods to simulate load. be careful, and i hope this helps.
