I probably in the minority that gave up a diesel for a gasser. I had a duramax dually pulling a 32 foot Cougar (GVWR 11k) did a good job but honestly the pin weight wasn't enough to settle the rear down and was always a little bouncy.
We downsized to our current 5er (9800 GVWR) and at the same time went to a 3/4 gasser with the 8.1L Vortec.
Dues to year model differences the Gasser has more hp by 100 and only 50 less ft/lbs torque.
I've towed both campers with the Vortec and prefer it to the LB7.
Don't let mileage too big a factor in decision, rather cost per mile. between my two the gasser goes 400 miles for $75 the diesel $76 due to fuel cost.
A bit confused on 30K for a used truck. I just paid $15K for mine with 62K on the clock. Mileage is more important than age in these trucks. I realize in New England age can equal rust so consider some long distance shopping.