CK5
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It'll cruise on flat level. Even a long easy grade will slow me down.
It pulls strong in the low gears to 3500-3600. Now I am considering a deep dive in my dist advance timing.
When matted my vacation advance can't be helping much. I get 40 deg at @2300 combined advance. Haven't checked mechanical only. Will check this soon.
Next, I might throw some plugs at it, these have been flooded a couple time recently.
 
You sure you aren’t rattling it? Higher compression and 40* is a lot to ask of shitty pump gas

Does make me want to revisit your cam timing numbers. What stick is in there?
 
Summit 1102. Also 91 pump with Lucas octane boost or 5gl av gas. Getting expensive.
Is 9° at idle
 
I think they are allready open. I spend a lot of time over 1/2 throttle.
Going to remove the tbi post pump filter. Inspect all my braided hoses for internal flaps.
The new fuel filters seemed to make a small improvement. St George to lake Havasu via Las Vegas. Mostly flat but a few long gradual grades to pull. Some I was able to maintain, a few the mph crept up 1 or 2 mph.
Next oil change going to throw caution to wind and advance the cam 2° bring the power band down a few hundred rpm.
Engine did pull in 3rd gear well yesterday. 3000 to 3750 rpm, 3750 is 66 mph.
 
Next time just borrow the engine out of the other Suburban.
 
I had 2 identical Suburbans same gears, same tires size,, one 5.7 and one 7.4 and my 7.4 gets 15% better mileage loaded or empty.
I got rid of the 5.7 truck
I’m sure I get people rolling their eyes when I say the 8.1 does as good as the 5.3 used to in my truck. But when you think about peak torque coming in much earlier than any small block it doesn’t have to be spinning at 3700 rpm to maintain speed in third gear with a load on it.

The more rpm you are pulling at a given speed the more fuel you are consuming.
 
With my suburban, tbi 5.7 sm465 4:10 gears on 37's i got consistently 6.5 to 7 mpg on highway trips.
Swapped to a 454 and qjet and wide 38's and averaged 11 to 12 mpg pulling a trailer thru texas. My mind was blown, it just did everything easier than the old 350.
 

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