last month i bought a beatiful 1998 gmc c3500 6.5 liter turbo diesel extended cab 2 wd dually. nice three door camper shell , original full length staimless steel running boards, really clean 2 owner truck only 119,000 miles. the problem simply is this... its too damn doggy! too slow, no power, and i took it too a reputable diesel shop in dcentral illinois for a pep talk and was told there is absoutely nothing that can be done to give it more power!!?? is this true? have i made the worse buying decision of my life??