Congrats on your purchase. Let me see...rumble could be an out of balance driveshaft, Ujoints, axle bearings. Depends on when it rumbles. Try a different gauge to confirm temps. 240 is too high. 260 is engine damage. You can send your VIN to Pontiac Historical Services and about $75 and they will provide you with documentation about what your car was when it was built.
