Need Help Fast Cooling System

Ok, Have A 99 Wrangler, 4.0 Inline 6, And The Problem Is Once It Hits The Normal Operating Temp(about 210), It Keeps Going Up. It Cools Down As Long As I Keep Moving, But Once I Stop, Or Hit Traffic(stupid Drivethru!!) It Will Rise The Temp Dramatically. Then When I Turn The Car Off, It Will Kick All The Coolant Into The Reservoir, Splashing It All Over My Driver Side Fender. I Have Replaced The Thermostat,(easy Stuff First) And Other Than It Kicking Out The Reservoir Vent, There Are No Visible Leaks. I Need Help Identifying This Problem And Fixing It. (oh Af Gods, Help Your Loyal Son!!!)

Ok I Realize There Are A Lot Of Lurkers In Here, But Would Somebody Please Respond? I Need Help. And I Know Some People Have Read The Thread, Because Of The Counter On The Main Screen.

How does the radiator look? Is it still the stock radiator? The tank on mine cracked at a little over 100,000 miles. Not only that but it was full of crap. Look around the tank for cracks and bulges, or leaks around the seams, where the tank is crimped on the radiator. Have you tried to flush the cooling system yet? Oh yeah, my jeep is also a 99 with the 4.0.

Ok, Have A 99 Wrangler, 4.0 Inline 6, And The Problem Is Once It Hits The Normal Operating Temp(about 210), It Keeps Going Up. It Cools Down As Long As I Keep Moving, But Once I Stop, Or Hit Traffic(stupid Drivethru!!) It Will Rise The Temp Dramatically. Then When I Turn The Car Off, It Will Kick All The Coolant Into The Reservoir, Splashing It All Over My Driver Side Fender. I Have Replaced The Thermostat,(easy Stuff First) And Other Than It Kicking Out The Reservoir Vent, There Are No Visible Leaks. I Need Help Identifying This Problem And Fixing It. (oh Af Gods, Help Your Loyal Son!!!)

Before getting into anything Jeep specific, go through the obvious stuff common to most cars/trucks with these symoptoms. I'm really not too familiar with this vehicle, but based on the symptoms I'd expect an issue with the cooling fan.

Is it a mechanical or electrical fan?

Electric:
If it's electric, does it com on when overheating? If yes, suspect a faulty water pump or head sealing problem. If no, you've got a cooling fan issue. Disconnect the plug to the fan and use a voltmeter see if you have 12V across the power and ground lines. If you do, but the fan won't spinn the motor is bad. No 12V would suggest: blown fuse or bad relay or PCM not commanding fan on, possibly due to internal fault or bad inut from temp sensor.

Mechanical:
Is any belt shroud missing? If not, replace fan clutch.

Non- fan related things to consider:
Has your water pump been replaced? If a low-quality el-cheapo water pumb has been installed, it may have a sheep metal impeller (like a fan blade) pressed onto the driveshaft. Sometimes the impeller will come loose causing poor flow at low RPM. Any noise, or failure to cool at low engine speed but cools when revving engine would be a strong indicator here.

On some vehicles, if you ignore a noisy (and bad) water pump for a long time before replacing it, it can damage whatever is behind it (timing cover, engine block, cylinder head, etc.) and that part will need to be replaced or you get poor cooling at low engine speed. To check this, remove pump and look for grindage type damage.

Jeep 4.0L specific problem:
The Jeep 4.0L from about 1997 to present has a known fault in the cylinder head. Frequently, the cylinder head casting will crack. Remove the oil fill cap and shine a very bright light down through the hole in the valve cover. I like to use a $10 compact 9-LED flashlight. If you see a crack in the cylinder head, replace the head and gasket with new ones.

I'd bet you have a bad fan clutch. The fans job is to keep the air moving when the vehicle isnt so if its staying cool at speed but overheating wwhen sitting still or slowly moving, My money is on a bad viscous fan clutch.
You can test your fan clutch (I havent found it to be an accurate test though).
With the engine off and cool, spin the fan and note the amount of force it takes to spin it, it should spin easily.
Now run the engine till it gets to operating temps (around 210), shut it off and spin the fan while its still hot. It should be noticably harder to spin.

I mentioned Jeep specific because BLAZERBOY69 stated he had already done all of the "easy stuff first". I would look at the obvoius first too, I addressed some of the common " jeep" problems to give him some better insight to problems these vehicles have.

Ok Here's A Little More Info On This. When Stopping, It Will Hold Temp Fine, But When I Take Off From The Stop, The Temp Will Come Up A Tiny Bit. It Will Go Down For About Ten Minutes, Then Start Inching Up Slowly. I Have A 45 Min Drive From Job To House(mostly Backed Up Highway), And Right Around The Half Hour Mark It Will Start Rising Above Norm Temp. I Drained The System About Three Weeks Ago,and Refilled It, Burped It, And It Was Ok. I Changed The Tstat About Two Weeks Ago, Because The Problem Started.

I think I would try flushing the radiator first. I would use the Prestone Heavy Duty cleaner. It comes in powder form. Its is super strong cleaner. You can also pick it up at a GM dealership under part# 12346500. I know this stuff will clean a radiator.