I have 94 ranger extended cab 4x4 4.0 auto....and I am a mechanic...not really engine mechanic,front end and exhaust....anyways,, ,was gonna put headgaskets on my truck.. tore it down both heads had cracks between valves....put set reman heads on....put it all back together.. cranked right up and ran great for couple days...now it has intermittent power loss,like won't take gas,like fuel filter kinda. Replaced fuel filter,twice cleaned iac put new gllenum gasket on,,no vac leaks as far as I can tell....if I'm on flat ground or downhill runs greT,but little hill kills it..I'm talking 35 mph... and fuel pump is about year old..please help

 

Vacuum leak somewhere?

 

Can't find one..have sprayed ether everywhere

 

After engine is warmed up and idling, unplug the IAC Valve's 2 wire connector, it will close
Engine idle should drop or engine may stall, either is GOOD, it means no vacuum leak, much safer than spraying flammable stuff around, lol

Can you test fuel pressure?
There is a schrader valve on passenger side of fuel rail
Schrader valve is whats use on tires for air

1994 should run 30-35 psi pressure, and should stay the same if you hold RPMs at say 2,500, if its slowing dropping then could be fuel pump or Fuel Pressure regulator(FPR) issue
"New" fuel pump would be suspect if its wasn't a Motorcraft brand, 3rd party brands tend to fail, but are way way cheaper

Compression = power
1994 4.0l OHV is 9.0:1 ratio so should show 150-160psi on static compression test
If possible test one or 2 cylinders just to take low compression off the table, or.................find out its the problem, so no wasting time, and money, on non-fixes
Low compression would be noticed more under higher load, like going uphill

Vacuum gauge tests, one of the better tools for engine diagnoses, and they don't cost much
At sea level to 2,000ft engines should run 17"-20" of vacuum

Good read here on some tests to do with vacuum gauge on ANY gasoline engine: https://www.gregsengine.com/using-a-vacuum-gauge.html

 

Unplugged Inc idle dropped ......can't test fuel pressure right now can't get in my work to get my fuel pressure testerr till monday...sane with vacumm.. it runs stronger than it ever has for about 5 to 15 miles....then goes to crap

 

Little different symptom there

So it runs better cold than after it warms up?

Or even if warm, i.e. restart, it runs better for 10miles or so?

 

Compression is good....fuel pressure is 29 lbs
..when u hold it at 2500 rpms it drops slowly

 

Reads like the "new" pump might be fading out

There is a "sock" filter inside the gas tank, that's usually changed with "new" pump, if its not you get what you have now, same as dirty fuel filter, because that what it is
Pump can't maintain flow in high demand