start with the basics. update everything that has not been recently tuned up. You can NEVER go wrong by keeping maintenance up to date (i.e. you have to do these things anyway):
clear your codes by disconnecting th ebattery for a couple minutes
champion copper spark plug
fuel injection cleaner (if you're running through a lot of quality gas, you don't need this. if you let the jeep sit for weeks at a time, then use it regularly).
clean throttle body
clean IAC valve (attached to throttle body)
clean all battery wire connections (both ends of each wire)
disconnet the fuel injetion wires one at a time, clean them with electrical connection cleaner spray, pack with dielectric grease, then reconnect. Do this for every other electrical connection you can find (although a FI connector is probably your issue with code 27).
I also wouldn't hesitate to run a can of Mopar combustion chamber cleaner through the engine. it's about $6 on amazon.
If there is no improvement, reread the new codes to make sure 27 comes back, then come back and we can run you through looking for frayed wires and node lights.