33 to 31 vs. 3.08 to 3.73

[kevinr1970]

On my ’86 GMC short bed 4x4 I have 33” tires and according to the glove box 3.08 gears. No reason to believe that gears have been changed.
I have a 305 (with headers) and a 700r4.

When driving the truck I can’t help but think the 305/3.08/33 isn’t the optimum combination.
I have a set of 3.73 axles on my parts truck.
I also have talked to a guy that said he would be interested in trading me tires for his 31’s. Tires are in about comparable condition.

What I am wondering is will either one make a bigger difference than the other?
My inclination is to go with the tires as we have a tire machine at work so it would theoretically not cost me anything (maybe a case of beer to the maintenance guy to grease the wheels if you know what I mean). I think that the 31’s would also be the same size as stock or closer anyways. This would get my speedo back right again (or closer).

The 33’s look better though and I think the 3.73’s would give it more “oomph” when driving it. There has been a fairly convincing argument for going with the taller gears as they would put the engine in a better power range at freeway speeds. Also require less effort to get the truck moving from a start. Theoretically netting better MPG; maybe not much but at $3.15 a gallon (and climbing) everything counts.
The 33’s would require more work and probably some money with brake fluid for bleeding the brakes. The front brakes on the parts truck need to be done too so turning the rotors and new pads, etc.
Also, not only is the speedo off because of the tires, but not sure how it would be affected by the gear change too?

Any thoughts?