Another guy here that agrees with keeping with what you've got.
2007 GMC Sierra SLE Classic 3500 dually, has 289K on it and runs like a top. I bought an extended warranty for it, covers the engine and drivetrain for 3 years. Yes, I've had some maintenance come up, but the basics are in good condition. It took me to the Grand Canyon and back last fall, high mountain passes (Wolf Creek) and high desert. No significant issues at all. Spent a little money to improve the aesthetics of the truck (dualiner bed liner/truxedo tonneau soon). Since I only use it for towing, it doesn't see a lot of daily drive wear and tear; have 2 other vehicles for every day and a back up tow vehicle (2003 Chevy Tahoe) if I need it.
