Loss of power

Your van has a 4G60 series(62/63/64) engine, and is now 25 years old. Loss of power can be caused by many things at this age. Most likely is worn valve stems, leaking valves, and loss of compression. Could be a failing head gasket. The first step is do dry and wet compression test, then a leak down test. If there is a lot of blue exhaust smoke, the engine is burning oil (worn head or/and piston rings). If there's white smoke, its burning coolant, and you have a blown head gasket.

Assuming the rest of the van is adequately mechanically sound, the best approach is likely rebuilding the engine with new rings, possibly rebore for oversize pistons, and a re-manufactured head.

random misfires can be attributed to low fuel pressures and faulty injectors
with out any details as to fault codes found, check the fuel pressure at the manifold ( around 65 psi)

engine check lights only come n they dont say vacuum leak,you have a blown head gasket

This makes me think of a loss of vacuum.
Afraid that you may need to go to a local garage to have this checked.

it might be misfiring problem,scan test & start from there.

watch engine RPM. if it rises real fast and car dont go up hill
that is transmission slip and btw can burn it up worse .

Overheating can be "boiled" down to a few issues:
*blockage: Something is stopping or slowing the flow. Main suspect is the thermostat. It is designed to open and close at the proper temperature so as to keep the engine at the optimum temperature range. They have a tendency to lock closed and cause overheating. Sometimes it's random. The blockage may be something like sludge or rust in the radiator or gunk that someone put in that does not agree with it.

*coolant/water loss. A leak somewhere. Blown head gasket, cracked head/block, hose, etc.
*pressure loss. This happens when the water gets to boiling temperature but is kept under control by pressure (pressure resists heat) and then something such as the radiator cap releases the pressure and the temperature rises. The coolant will also leak out and then the overheating will be due coolant loss as well. This is especially true with the Cadillac Northstar. The head bolts allow the head to lift off the block, ever so slightly, and pressurize the coolant system with exhaust gases beyond radiator cap pressure limits. It's usually when you accelerate or put the engine under load such as going up hill.

^check for exhaust gases in the coolant. smell it or buy a kit to test.
^get a new thermostat, or, test the old one by boiling it in water on the stove; see if it opens. I always get the "failsafe" kind: fails in the open position.
^check for oil in the coolant or coolant in the oil: grey sludge.
^check for leaks on the ground.
^test the radiator cap. some part stores have a way to test them.
^check to see if it's made by Cadillac. look for the word Northstar. If so, hold on to your wallet. There's a whole new world of overheating adventures.

ANY DTC'S ?
CHECK ENGINE COOLANT TEMP. SENSOR 2 WIRES YELLOW / BLACK
SHOULD BE ON INTAKE NEXT TO THEMOSTAT (V8)

it could equally be all of those things. You would have to test them all. it could also be that there is a hose that goes to the radiator that could be kinked

check for a failed cat converter
run the fault codes as items that look good seldom are