Supercharge or gear swap?

[ASTAR]

Ok so I Love my new Hummer but the mileage sucks (I knew it would so no biggie) and the power is lacking. I went from a 700hp/1400ft lb tq Dodge diesel truck to this and man, what a difference. I am not expecting to have a hot rod like my Dodge was or the tow master it was either but....
Something I can't deal with is the lack of being able to hold 4th gear on the freeway at speed. If I am doing 70-75ish and there is the slightest incline, it slows down (cruise on or off) and then downshifts to 3rd to hold speed. Its constant. I have 38" tires on it now and I know that made it much worse. I did the small engine upgrades (see signature) but it still sucks badly.
Ultimately, I would like to gain seat of the pants power and can't decide how to do it. I was thinking about putting 4:88 gears in it but wonder what will happen to my fuel mileage. It was around 11.5 before lift and now around 9 with the lift/tires. Maybe a supercharger (yes I have been searching) but the transmission scares me. I don't want to dump another 10 grand into this thing between the upgraded tranny and supercharger itself. What will the MPG do with a supercharger if I did though?
I also tow about 7k once or twice a month. Not a big deal but if I hit a hill, whoa, it hurts. The MPG drops hard and the power is seriously deprived.

So whats the word from the masses?
I figure I can install the S/C if I go that route and maybe I can talk GM into helping out some with a tranny if I smoke it? Maybe? I'd also return the Airaid and Hypertech if I supercharge (money back) since it's only been on for about 2 weeks. Gotta Love Summit!
If I do the gears, I'll have to have them done as I don't know how to "set up" gears.
Seems the gears would be a lot cheaper and more warranty friendly but will I feel the power again? Will I have horrible MPG since RPM's will be higher in O/D on the freeway at 75mph? I'll also be keeping the Airaid and Hypertech if I re-gear.

Any input is appreciated, I can't deal with this downshifting!!! HELP!

Thanks.