I've driven (all 4wd/4cyl): 2nd gen ext cab manual and auto, a new SR auto and manual, and a regular cab 2nd gen manual at fairly low elevations (Appalachian Mountains).
-2nd gen ext. cab manual. and new SR just adequate
-Auto new SR and 2nd gen ext. too sluggish.
-Regular cab: 4cyl manual worked excellent and had a bit of pep...reminded me a lot of driving my old 22re regular cab 4x4 on stock tires with a header.
The weight is really noticeable on the new SR with the 4. Unless you are looking at 05-14 regular cabs, I would avoid the 4 or plan on getting a 2nd gen ext. cab and doing a couple of bolt ons especially since you now live at elevation.
The gas mileage penalty of a tundra is pretty minimal when compared to the V6 taco. Especially with any kind of load so...
For me, my next replacement will be:
gently used (rare) Tundra RCSB with the 4.7L/5speed auto (excelllllllllllent truck....don't drive one

)
RC 2trfe 5 speed 2nd gen with the lowest miles I can find in the country (would replace my Fit and Sport)
or a 1st gen tundra 05-06 RCLB
2015 left over Outlander GT (if I decide a wagon with ATs will work)
03+ minty Montero
or buy 8 more Montero Sports for the money...
or keep what I have and continue being "budget conscious" :elkgrin

as a salesman politely referred to me being a cheapskate).