so i have a 96 xj 4.0 HO. while in idle the temp tends to climb as it does this the car will start to shake. feels like it is about to die. ive been told to change my thermo. wondering if this is a good idea? maybe a rad flush also?

 

With cooling system maintenance, it is "pay me now" or "pay me a LOT MORE later".

How many miles and years on the coolant and stat? What COLOR is the coolant?

It is never a bad idea to do a flush and fill and a new 195 degree thermostat.

How about a new radiator cap? They're only $5.00. Spring for one or at minimum, have yours pressure tested. You want a 16 pound cap, and skip the pressure release lever. Not necessary and another point of failure for a cap.

Also, the #1 cause of "temp creep" at idle is the FAN CLUTCH. Easy to replace, inexpensive and overlooked plenty.

The other symptom you mention (shaking and about to die) may be something else. When was the last tuneup? Fresh champion copper plugs gapped to .035, new wires distributor cap, rotor.