Ideas for Power and parts needed

I just got a 94 suburban that is basic (no tape player or anything)...anyways looking for 2 seat belts for the middle seat (mount to the side type prefer blue) and also looking for new speakers (the old ones make a weird buzzing noise...any ideas?)...also looking for ways to get more power, and better gas milage (did i just write those in the same sentence? lol..sencond is more importaint)...its fuel injected..also getting ideas on nerf bars/step ups...price ideas? is it best to get them off line or a parts store? Its white with all back trim and black windows...anything i should know about them? Its a 2500 and i bought it for my boyfriend to tow his racecar trailer.