Check your shocks for wet spots indicating leakage. Check each leaf spring for cracks in any of the leafs. The rear shackles are a known weak spot on early model Titans, so check the bushing area as well as all the parts of the shackle that are welded.
One question: Do you have an aftermarket exhaust? I had squeaking from the rubber hanger near the exhaust tip due to the exhaust slipping rearward (loose exhuast clamps). When I repositioned my exhuast the squeak went away.