Diagnose 93 Suburban C1500 engine "skip" under load (towing)

[ker]

93 5.7 C1500 193k miles: On the highway pulling a 1 ton trailer and typically under a load (e.g. climbing a hill) my engine will periodically intermittently skip - a definite abrupt loss of power for an instant. I've only noticed this while pulling a trailer and under load. I've checked and cleaned the Distributor cap, rotor and PCV valve; checked the plugs & replaced the fuel filter. Fuel pump was replaced about 4-5 years ago.
Out on the highway without the trailer, I've not noticed this happening at all.

Additionally, on a trip last week, this behavior occurred and also my first tank full gave me 15 MPG and the second one on return gave me only 12 which is far less than I've ever gotten before. I usually avg between 15-17 when on the road with the trailer.

Since this is load related, I'm not expecting an ignition problem but something else.

Anyone had similar behavior and can offer any suggestions? Thanks.

 

[Fordum]

Need to get a scan tool and pull any codes. Also you can leave it plugged in and watch for problems as you drive.
Let someone else drive or watch. Don't try to do both.

This is a real long shot. I have only heard of it once, and when I mentioned it here most folks did not think it would happen.
But, knock sensors can be fooled by hard vibrations from another source. The one time I saw this was a really loose homemade trailer hitch that let the trailer slam and bang on the frame as it went along the road.

The vibrations were interpreted by the knock sensor as a knock and it would retard the timing and cause a loss of power.
I doubt your hitch is that bad, but if it was a pintle type hitch, I could see it happening.
But, I would expect it on level ground, not when all the slack was out going up a hill.

Either way, you could see the knock count go up with the scan tool.

Otherwise, I would suspect fuel issues. Sounds like you are calling for more fuel than your system can deliver.
Pump or filter.

 

[4xcrazy]

Alittle different engine, but the 4.3 would "skip" at times only under a load, acceleration or whatever, I replaced the fuel pump & filter, dist cap & rotor, spark plugs, but the one thing I didn't replace was the wires. It ended up being one wire grounding out behind the block somewhere.