1999 Jeep Cherokee

Is it a linkage problem? Or shifter is in reverse and wont move? What do you mean by "pushes very hard? Fast idle? If check engine light is on try this to retrieve the codes. You can try a self-diagnostic test. To activate self diagnostic program:

With the ignition switch in the OFF position, depress the TRIP and RESET buttons.
While holding the TRIP and RESET button turn the ignition switch to the ON position.
Continue to hold the TRIP and RESET buttons until the word CODE appears in the odometer windows (about five seconds ) then release the buttons. If a problem exists, the system will display Diagnostic Trouble Codes (DTC's). If no problem exists, the code 999 (End Test) will momentarily appear. If this does not work, get the two digit codes by turning the key from off to on three times, and on the fourth time leave it in the ON position, codes will flash on the check engine light. Count the flashes.22 would flash as 2 blinks, then a short puase, then 2 more blinks. If several codes are stored, the pause is longer between codes, code 55 will be the last code. Do this and post all codes found.

Have the pressure checked, reverse takes more pressure than drive gears, the pump may be on the way out.