Intermittent sudden loss of power on highway

[Mik3]

I'm having a very strange problem that I've never even heard of. I've been testing and researching but nothing has come up yet.
Here's the problem:
While driving down the highway, at anything over 60, the engine will eventually lose power after maybe 10 minutes of driving at 60mph plus. I can drive at 55 and no loss of power depending on load(climbing or not). But the strange part is... I can force the power to come back...... When it loses power, if I make it downshift and push the pedal just a little harder, the power will regain to normal after maybe 3-5 seconds. I let off on the pedal just a hair and back down on power, push a little harder, and boom its back just like clockwork and I can repeat this every time. It will lose power every time I go over 55, and I can make it gain power back every single time. However, the pedal has to be far enough down to regain power, the only way it will drive normally without pushing the pedal harder is if it gets a break(pull over, let it idle or just drive at 50 until the power regains). But it seems to lose power only at 60mph and higher.. I can romp the out of it through town and no problems.. as long as it's not at highway speeds, its fine. I've hooked up my scan tool and observed all the sensor readings while its driving normally, and when its losing power, and they all seem similar, so I'm not sure that it's a sensor issue. The one thing I haven't done yet is do a fuel pressure test while it's happening, I'm going to... but I need some suggestions for things to test. I'm stumped, it seems to be a fuel delivery issue, but if it is... why can I force it to regain all power just like that?

1997 GMC k1500 with the 5.7 and 4L60E. 213k on the dash. I've driven the highway alot with this truck alot and it's never done this until recently.. I use to haul 90mph every day to get to college, never had any power loss. If anyone could throw in some advice.... It would be much appreciated!

 

[IOWNJUNK]

Fuel pump gets my vote.

 

[dowsewashere]

Id start with changing your fuel filter and if it doesnt help id wait it out and see if the pump dies.

 

[michael hurd]

As said fuel pump and or wiring could be an issue or even a partially plugged convertor. The next time that happens pull over and take a look at the convertor body, if it is glowing that is not a good sign. Ignition coil can cause issues similar to that but it would be at high rpm and load. A coil would cool off and act normally if you shut the vehicle off for a short period.

 

[Mik3]

My fuel pump is a wining little ................ so, tomarrow or friday I'm going to be replacing it. If that doesn't cure the problem, I'll go ahead and replace the coil just cause, I've tested and diagnosed, it may be time to just throw some parts at it, never hurts to put brand new parts on her. I refuse to let anyone work on my truck because there's alot of half ass morons in most shops these days... So, bringing it to a shop to get diagnosed is out of the cards.

 

[SCOTTYINWV]

Sounds like you are either leaning out or are getting spark knock, causing it to retard the timing causing the loss of power. I would lean toward fuel first though.

 

[badazzbulldog]

I went thru this issue recently before doing the pump disconnect the return line to the tank and disconnect it where it connects just under the drivers side floor and put air to it and see if its blocked,never thought to check it when I did the pump which in turn a month or so later caused the fuel pressure regulator to go bad,also check for small vacuum leaks around the upper plenum of intake a small leak can cause the lean issue