Top Speed Low ET
John is right to ask for more info to zero in on what may be ailing you. To give you some info the roll around, If you want to go as fast as you can in near any combination, the torque converter needs to be as loose as the traction ability of the car can handle. A 4000 stall will net better ET's than your 3500 one will, but the MPH may diminish........ possibly. You want to have the converter in just below peak torque RPM and flash just over it in a drag car that is pursuing best ET performance. You may have 10 other problems that are not on our radar with out more info though, but this rule of thumb may give you something to look at for your next purchase.
Bruce