Ram W/Intermittent problem with sudden loss of power

I am experiencing an intermittent problem with sudden loss of power and bogging down. With my 95’ Ram 1500 (318 140k) at freeway speeds engine suddenly loses power and runs terribly and will run only with minimum throttle and with too much throttle will backfire and possibly die after I pull over and wait five to ten minutes engine will usually run perfectly again this problem can happen after five miles or five hundred in hot or cold weather. I do not smell any gas fumes
In fact I first had this problem in Florida and it resolved itself then drove to California with no problem now problem is back I have replaced EGR and control solenoid (found it melted due to contact with exhaust system), cat converter, temp sender, and a few other sending units checked for exhaust obstructions. I also noticed that there seems to be a vacuum in the fuel tank when the problem occurs if I loosen fuel cap I hear air rushing in past the cap? The cap passed the cal smog test but I have replaced it with a new Stant replacement still get vacuum or possibly pressure but it sounds like a vacuum is this normal could a vacuum be forming in the tank and causing the fuel pump to be slowed or stopped? Maybe that would explain the intermittent problem at freeway speeds? And now just replaced Evap purge solenoid but problem remains there are no trouble codes being generated. Any ideas would be greatly appreciated since my girlfriend lives around 300 miles away and this could happen a couple times a trip!
MORE:I have now changed out crank sensor, cam sensor, rerouted wires per tsb, new stock coil, changed out Bosch platinums with stock plugs, changed out gas cap, bought fuel pressure gauge pressure at spec. The problem with engine bogging down still happens after long drives at 65-70 mph I live in California and want to drive to New Orleans to help victims my prevous post have not gotten any replies please respond it you have any ideas.

Not sure if related but since I changed out gas cap seems like moisture actually water accumulates in cap?

One of you guys must have an idea.