I4 loss of power and rumbling up hill only

While towing just under 3000 lbs 2 weeks ago, going up a very long steep grade on highway, I began to loose power and seemed like the engine was going to blow up. I got off the highway and proceeded to drive at slow speeds on back roads. Truck has been pretty much normal except when I try to push it up long hills it starts to bog down and a rumbling starts shaking the whole truck. What could be causing this?

 

Plugged cat? Is yours a manual or auto?

 

Good flow out of exhaust. It is a 5 spd manual. Has 240000 miles

 

Take it on a highway....put it in third gear and speed up till about 3500-4000 rpms...if the cat is starting to go it will start to hiss as it's compressing the exhaust manifold bolt springs to let the air escape.

Also how is the condition of your clutch?

 

Clutch hooks up well, but throw out bearing makes noise when going from reverse to 1st. Exhaust system is a bit undersized in general. I let a cheap muffler shop put a universal muffler on with a short side exit to pass inspection a year ago.

 

The cats are about 5 years old. Had them replaced by dealer after they were stolen.

 

Pop the number 4 coil out and if the tip is covered in oil it’s time for valve cover and spark plug tube gaskets. Then I’d replace the plugs with

$39 NGK 6619 Iridium Spark Plugs LFR6AIX-11 - 6 PCSNEW

NGK 6619 plugs and buy new Standard Ignition Blue Streak UF495 ignition coils. It worked for me. Good luck!