Overheating, I know what else is new
 

1996 4.0 blahdee blah.

New thermostat, fan clutch, water pump, two core radiator, flushed and filled. Runs for about 5 minutes before climbing to 210 then slowly all the way to 260. I'm trying to figure out why and also why there is never any pressure on my top radiator hose ever. Slowly losing my mind with this thing.

Hate to be the barer of bad news, but with the symptoms you're describing, I'm thinking either a blown head gasket or a cracked head.

Edit: Wait a minute, backup on my part. If you aren't getting any pressure in the upper rad hose, then that means coolant isnt flowing properly. Is the t-stat housing clogged? Is the new t-stat a fluke?

I had the same thing happen to me. It ended up being a large air bubble somewhere in the coolant system. I parked on a steep hill with the front end pointing up. I disconnected the Heater core hoses and left the radiator cap off. The bubble finally came out.

Where did you disconnect the hoses at, the heater valve thing, or the t-housing? Was this with the vehicle running or off?

I disconnected the hoses at the T-housing and the vehicle was not running.

I thought I would mention in case you didn't know. There is some kind of hole or indent in the thermostat that needs to be on top when installed to aid in releasing trapped air bubbles, I would double check that and also would replace the rad cap just cause.

I'm working through the same situation right now dude. I plan on following up on previous threads when I fix my issue. Please do the same here. Best of luck to you.

Looks like you did everything but bleed your system of air, park with nose up running, heater on full rad cap off let it get up to temp. add fluid when ever it gets low repeat till fluid stays at full and no more air bubbles come out. just like Nicksdsm said air in system.Try and follow up to let us know if it works everyone should follow up.

OK so far, New radiator, water pump, coolant temp sensor, thermostat installed with air bleed hole facing up, new radiator cap, new fan cluch and electric fan, and new heater bypass valve and hoses. Now it seems to run cool but the gauge spikes almost immediately. Going to replace the coolant temp sending unit and get a mechanical gauge to check as well. pretty sure this is the end of the road for me.

bad sending unit giving false readings. All is well running 200ish. Thanks guys.