1991 S-10 4.3 L 4x4 pu

Because of the lifter noise, I think that you have valve problems which are causing the backfiring. If the camshaft lobes are damaged or the intake valves are not closing properly it could cause backfiring. Check compression and with the valve covers off, check to see that the valves are moving properly. If you want to find a GM specialist, here's our directory link for you: https://repairpal.com/chevrolet-repair-in-rustburg-virginia

probably wiped the lobe off the cam