Where to replace coolant temp sensor for 1998 grand jeep cherokee

no---it cannot be by passed
it's purpose is to report the coolant temperature to the ECM which in conjunction with the ambient temp sensor , BARO sensor allows the correct setting of the air/fuel mixture setting for the current settings
It also reports for an engine light when the engine exceeds the boiling point of the coolant

That code is for the engine coolant temperature sensor. "...input above maximum acceptable voltage." I would try a new temp. sensor. If that doesn't fix it, you may need to have an engine scanner hooked up, and see what the sensor is sending to the computer, and go from there.
A bad coolant temp. sensor can cause hard starting like your symptoms.
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Trace the upper radiator hose toward the Grand Cherokee's engine until you reach the metal component connecting the hose to the engine -- this is the thermostat housing. Find the coolant temperature sensor -- the electrical component on the thermostat housing. Press the locking button on the coolant temperature sensor wiring harness and pull the wiring harness from the sensor, then remove sensor it screws out. when putting in new sensor coat the threads with teflon pipe thread tape so there is no leaks.

4.7L ENGINE CRANKSHAFT SENSOR LOCATED ON THE ENGINE BLOCK ABOVE THE STARTER. ON THE 4.0L ENGINE CRANKSHAFT SENSOR LOCATED TRANSMISSION BELL HOUSING AT THE LEFT REAR OF THE ENGINE. THE 5.2L 5.9L CRANKSHAFT SENSOR LOCATED ON THE ENGINE BLOCK BEHIND THE RIGHT CYLINDER HEAD.

in the 5.2L V8 engine the coolant sensor is located on top of the engine. Locate the coolant thick hose coming from top of the ratiator to the top of the engine. Look at the place such hose connects to the engine you wont miss the sensor it is about one inch from there.

Should be near the thermostat housing

Have you checked the coolant temp sensor. They also have something called a MAP(manifold absolute pressure) sensor that could be causing this issue. This sensor will have a 4 pin connector and 1 vacuum line going to it. Should be on the firewall, just behind the engine.

should be on the radiator.look on sides of radiator for 2 wires.they will be connecting to coolant level sensor.

If you changed the coolant temperature sensor and it had a 5 volt ref signal to it then you replaced the wrong part. You need to replace the coolant temperature sending unit.  The coolant temp "sensor" is an input to the ECM for your fuel injection system. The coolant temp "sending unit" is for coolant temp reading at the gauge, It is an NTC switch (negative temperature coefficient) which means as temp increases/resistance decreases. 

Yes, there is another one. The one you replaced is the coolant level sensor. The ECT (ENGINE COOLANT TEMP) sensor is located near the thermostat housing. It has a 2 pin plug on it.