Inevitably, someone always asks how big of a tire you can put on a Gen1 Monty or Raider and we always point people at the tire fitment chart, and rxinhed shows all his different configurations and says how great they all are. Then, someone almost always chimes in and says "If you go with 31's you'll lose tons of power, 33's will be a LOT worse" or something similar.

My experiences:

The truck: 341k miles, 2.6L 5 speed Raider. Stock, no mods.
The tires: 31x10.50x15's on 15x8 steelies with unknown, but wide offset.

I started off with the stock 28-ish tires, then went to 30's. The first thing I noticed was the that the truck sat just a smidgen higher. Cool. I didn't notice much difference except that it betrayed a worn idler arm with a slight wobble.

Then I went, a year later, to 31" tires. Again, it sat a little higher. Cool. I notice a bit of a difference between 30's and 31's.

The positives:
The 31" tires seems to compensate for what I consider to be too-low of gearing in these trucks. Stock is 4.62 gears! With 31's, over the original 28's, its the equivalent of swapping in 4.17's, which is much closer to the 4.10's that many trucks come with, and I find that the truck is quite a bit peppier when I'm up to speed. From a dead stop, the difference is minimal and if the truck is on level ground or even the slightest downhill, I can start in second if I want to. The truck is in its power band at more common speeds, and I can now zoom up steeper hills doing 55mph (indicated on speedo, not corrected) in 4th gear whereas I before did 45mph in 3rd. I personally think this has to do with matching the power band of the motor to where its needed, a lower down in the RPM range for the same actual MPH.

The negatives:
As mentioned my truck is very high mileage. I know it needs a ball joint and a TRE to be perfect. With the 30's I hardly noticed, but with the added weight and width of the 31's, I notice. The truck pulls a little now. But thats not the tires fault.

I'm at 4500' in the Reno NV area. Next week I'm moving very close to sea level in Washington state, and will report any changes that I notice over time with the higher air density there.

Overall, I am VERY glad I put 31's on my Raider and I'll do it again in a heart beat. In fact the next tire will likely be 33x10.50's if I can afford them.