I have 2 trucks that are doing the same thing 1 is a 93 dodge d350 with 360 the other is a 97 GMC Sierra 1500 with the vortec 350. The issue is that when cranking it acts like the timing is way off and the motor turns over slow slowing on each cylinder like the exhaust valve isn’t opening on time. This issue is intermittent. Sometime I start them and they run perfectly. Sometimes it starts and has pretty much no power  banging and popping at more than 1/4 throttle and sometimes they won’t start. I have done plugs wires cap and bug and fuel pump on both. I’ve tested for spark on both and fuel pressure and they both spark as well as have plenty of fuel pressure. I’m not sure what to do as I’ve never encountered an issue like this that’s intermittent