Shift, add throttle smoothly. Too much torque applied suddenly will snap the car into power oversteer. This practice was used when racing brake systems were marginal. If engine rpms drop below the power band the engine lugs. It takes a long time to regain rpms and lugging causes premature internal engine wear.
Check clutch and shift linkage.
Any slop translates into inconsistent shifting. Clean and lube frequently. By using a light weight, small diameter, low inertia flywheel-clutch assembly, the engine will accelerate faster. The part will move faster. Clean all parts and use a new radius faced throwout bearing.