What could be the problem? HELP ME PLEASE!

I have a 91 old 88 royae. I had an issue with the harmonic balancer and had it
replaced. Since then im having issues cranking it up initially. When I first go out
to crank it, the engine turns over, jumps, and makes a backfiring sound but
won't crank. After maybe three attempts the vehicle will crank but runs as it its
skipping. Then while I'm driving, initially, there is no problem but once the
vehicle warms up, it begins to accelerate extremely slow, jumps sometimes
while accelerating, and makes a grinding or whining sound only when I press
the accelerator and when I ease off the accelerator it stops. I have no ideal
what the problem could be. Can someone please help me??