First, I have to ask who told you that a copper radiator cools better? Aluminum is much better, that's why you see them in high performance and race vehicles. That being said, let's go after the heating problem. Start with the obvious and check the coolant level in the radiator. From there check the heater hoses - are they both as hot as the radiator hoses at operating temp? One hose will be about 15-20 degrees cooler because of the heat transfer from the core if the core isn't clogged. Your symptoms really make me thing the t-stat is stuck open but we need to check those things first.
Oil pan gasket removal:
- Disconnect the negative cable from the battery.
- Raise vehicle.
- Drain engine oil.
- Remove left engine to transmission strut.
- Remove oil pan and one-piece gasket. The engine may have to be raised slightly on 2WD vehicles.
- Remove the oil pick-up tube assembly. Discard the gasket.
- Fabricate 4 alignment dowels from 5/16 x 1 1/2 inch bolts. Cut the head off the bolts and cut a slot into the top of the dowel. This will allow easier installation and removal with a screwdriver. Install the dowels in the cylinder block at the four corners.
- Apply small amount of Mopar® Silicone Rubber Adhesive Sealant, or equivalent at the split lines. The split lines are between the cylinder block, the timing chain cover and the rear crankshaft seal assembly. After the sealant is applied you have 3 minutes to install the gasket and oil pan.
- Slide the one-piece gasket over the dowels and onto the block.
- Position the oil pan over the dowels and onto the gasket. The engine may have to be slightly raised on 2WD vehicles.
- Install the oil pan bolts. Tighten the 1/4 inch bolts to 11 N·m (96 in. lbs.) torque. Tighten the stud bolts to 16 N·m (144 in. lbs.) torque. Tighten the 5/16 inch bolts to 16 N·m (144 in. lbs.) torque
- Remove the dowels. Install the remaining 5/16 inch oil pan bolts. Tighten these bolts to 16 N·m (144 in. lbs.) torque.
- Install the drain plug. Tighten drain plug to 34 N·m (25 ft. lbs.) torque.
- Install the engine to transmission strut.
- Lower vehicle.
- Connect the negative cable to the battery.
- Fill crankcase with oil to proper level.
As for intake porting, I don't think it's worth the effort on a stock engine.
The thunking noise is a good one since it doesn't happen for a few seconds after the truck stops rolling. I think I would start by checking the engine and trans mounts.