[RyanAK]

Well, I thought I had this licked, but it’s back. I’m on the home leg of a 1,200 mile round trip to Maine to fish and it’s been slow going. Several pull overs and I’ve had to play the momentum game to get up over the hills. I really need to lick this. My truck is completely drivable around home, but long trips like this aren’t happening again until I get it fixed.

Highway speeds of 60-75mph, at load (uphill or long periods of acceleration), the truck gets starved for fuel. It bogs and goes in quick time, and feels like it’s sucking more gas than what’s available.

I added a “diagnostic tool” in the way of a vacuum gauge to help figure this out. I’m good as long as I keep the load to where there’s 10” or more of vac. Unfortunately this can drop my speed to 50 mph or less on a grade... with traffic zinging by at 75. If I spend any time with my foot in it and vac is below 10”, eventually it will start stumbling. When it bogs, the vacuum drops. So if I’m climbing a hill and engine vacuum is at something like 7”, when it starts lugging the gauge will bounce in time with the lugging between 7” (power) and 4” (stumble).

Engine temps remain steady. Ditto oil pressure. Idles fine with 20” at 750 rpm. It’s been hot and muggy.

Stuff I’ve done on this trip to try to improve things:

Air cleaner lid flip (to bypass the valve in the air cleaner)
Wired the choke open (thought the choke could be closing and choking the engine)
Insulated the hard fuel line between the fuel pump and carb where it sneaks between the block and alternator with rubber fuel line (hot fuel?)

Stuff I’ve done in the last few months chasing this:

Complete ignition tuneup (plugs, wires, cap, coil, rotor, module)
Timing dialed in
Idle air/fuel mixture
New fuel pump
New fuel filter
New soft fuel lines at pump
Confirmed clear lines from tank to pump
New air cleaner
Moved vac advance to manifold source
Double shot of Sea Foam
New PCV valve
New divorced choke

My suspects at this point:
Hot fuel?
Hot carb?
Coolant thermostat too high?
Exhaust heat riser valve?

My MAIN suspicion is that the truck came from Montana and is now on the East Coast. I’m not a carb guru, but I’d guess a rig set up for elevations between 3,000 and 6,000 ft in cool, dry air would need adjustment for a humid summer at sea level to 2,000 ft. Jetting, float level, etc.

I have a fairly decent tools with me and could use some guidance for moving forward. I’m at my non-mechanical in-laws in Connecticut today and tomorrow and would like to get this licked before heading on the last leg home to Pennsylvania. I’ll do just about anything I can under the circumstances, up to and including slapping a different carb on it to get me home. I really, really appreciate the help!!