I'm still having trouble with my F150 with the 5.0 engine pulling a lite load. It has 214000 miles and runs great up to 80+ mph but if I'm pulling even a lite load up hill (4% grade) it starts to shake and lose power to where I'm only able to run at 40 MPH under WOT. Cat has been removed and new muffler and pipes installed. Helped a very little. Burn a little oil like 1 quart in 1200 miles. Maybe valve job needed? Goes through coolant like crazy. 1 quart every 300 miles. No leaks,new rad. an hoses. Exhaust is smokeless. I'm stumped.

 

The shake is possible mis-fire. Mis-fire is often bad plugs or wires. How long since a tuneup? How long since fuel filter change? Start with the simple stuff. Find the coolant leak. Possible internal leak.

 

Full tune up done one year ago with fuel filter. Fuel pump pressure is good,new wires,dist,cap all done. That's my problem. All the work done and still missing and loss of power. I had a 13' travel trailer I rebuilt but sold after pulling it 30 miles and couldn't go faster than 40 mph up a 3% grade. Very frustrating. Normal driving around town it's great.

 

There is the smoking gun.

 

x2 ... start with a compression check.

 

Oil is clean no drips and no smell of gas in radiator.

 

Do a leak down test and check for bubbles in the radiator.

 

Look for visual signs of head gasket leak, it's pretty easy to detect.

You can test coolant for hydrocarbons, but it doesn't have to blow into the radiator in order to suck coolant, especially if the majority of the coolant seepage happens after shutdown.