1999 GMC Jimmy Do I have a blown motor

I just had the fuel pump replaced last winter.
Yes I did just fuel up but tank is not full.
I wondered if I may have jumped timing

Thas is what I have been thinking it is, the timing thing. Just by the way it runs. I am planning on doing a compression test this weekend, just to rule out what another guy said it could be. He said I had burned a hole in a piston.
The only code I got from the QBDII tester was a P0300. A random misfire on all cylinders.
Once I do the compression test, is there a simple way to check the timing. I was told I could take the distributor cap off and rotate the cam counter clockwise then back and watch the rotor while I am doing to see if it moves freely or there is hesitation.
Does that sound right?
And yes I agree that just because I replaced the fuel pump module last year, it does not mean it could not gone bad again.
I try not to ever let the tank go below a quarter.