The 5k tow rating is with a bumper mounted ball. I know with the frame mounted reciever hitch it's rated much higher. I'd look at the sticker in the door jamb of mine, but it's so faded I can't make out a thing. As for not having the power to get up to a decent speed, I bet you have the 3.42s. You could also have engine or tranny problems, because my 97 with 3.73s tows my toyhauler just as well as the 2004 GMC K1500 crewcab with a 5.3L and 3.73s I got rid of several years ago.