Dodge Ram Van 1500 high temp, no high speed

Year 2000 Ram Van , V6 model 1500.
Serious problems... Could water pump or oil pump be seized ??

Sat with full tank of gas all summer(5 months), previously all ok.

Poor running & unable to get up to speed ( 40 MPH max, flat out !! ).
( stalled several times, never did that before ).

Suspected bad gas so added Penzoil fuel system cleaner & an octane booster.

Drove for 30 miles on highway.
Engine quickly overheated (to red zone , greater than 270 degrees on dash gauge).
slowed down & took it home.

Next morning:
Checked oil : good & clean (was changed at beginning of summer).
Checked rad fluid: reservoir & Rad itself: all topped up
Trany fluid bright red.
Turns on for 1 minute, runs rough & feels like a slapping sound...

Pcodes:
P1682
P0300
P0304
P0305
P0305

From what I understand this does not tell me much, (misfires...)
Dash Battery meter reads +14V, so do not think this is significant.

Something is seriously wrong for the temp gauge to pin all the way to the right side.

Possible Plan:
1) Have dealer drain old stale gas tank( 25 gallons, full at present)
2) Cooling system check or just replace water pump, thermostat & radiator(corroded, but no apparent leaks) ?
3) Oil pump check or just replace oil pump ?

Ram Vans have had their own specific poor quality issues, so:
Please, only Dodge Ram Van experience or expertise.

thanks

Two things to check right away yourself is fuel pressure, may need to borrow or buy a gauge and check that the exhaust isn't restrictted, you can do this with a vaccum gauge hooked to a port on the intake, rev the engine to wide open in park and see if you generate any positive pressure on the gauge, if you get like 2 pounds or more then remove the upstream 02 sensor or remove the exhaust from the manifolds and retest. If it revs up then likely the catalytic converter is plugged, This can cause the misfires, obviously the gutless performance and can cause the engine temps to be too hot. If it has no effect then you need to verify the fan clutch is working properly, the cooling system will circulate coolant and verify that you don't have a headgasket leak. I wouldn't bother draining the fuel until you are certain you need to and if the pump will pump fuel then you don't need to siphon, just wire thee relay closed and hook a line to the test port on the fuel rail and let it do the work for you. Don't be too hasty to disregard any advice or info on this site if it's not an exact repair to your own vehicle, Most vehicles work the same, that engine and truck has the same failures as a 5.2, or 5.9 in a truck, jeep, durango , Dakota etc so read the forums for misfires on them and familiarize yourself with the successful repairs others have found. Most vehicles work pretty much the same for overheating issues and drivability issues so all advice of reasonable intelligence is to your benefit. If you don't own a Haynes or Chilton manual for your truck then start with one of those