Rainier is available with a standard, 275 hp, 275 lb. ft. of torque, 4.2 liter six cylinder engine or an optional, 5.3 liter V-8. The eight makes 290 hp and 325 lb. ft. of torque. Both are coupled to GM’s four speed automatic transmission. GM’s 4200 I-6 is adequate all around, but the 5300 V-8 feels far smoother and less stressed. There is a modest gas mileage giveback (comparing all wheel drive models, the six rates 15/21 city/highway, while the eight gets 14/18 mpg’s), and a not too modest price bump ($1,500 to step up to the V-8). However, amortized over the life of your car loan, I think that the dollars will matter less than the overall driving satisfaction of the larger motor. This is especially true if you tow. Rainier with the 4.2 will pull up to 6,200 lb. (4x2, 4.10 axle), while the 5.3 can be equipped to handle as much as 6,700 lb. (4x2, 3.73 axle).