I have a 1990 jeep cherokee with the 4.0 but I think I want to put in a High Output. What kind of gains should I see if any and what should I need to swap out to make it go>  

If you are seeking more power because of lift with big tires and stock gear you will see much more bang for your buck with regearing axles. Cherokees tended to be geared pretty tall for factory to begin with and a new deeper set of gears will give you a far bigger seat of the pants power boost than a 4.0 HO will.  

ya. I got 4.10 front and back and both axles are locked. Im looking for power. Soooo back to asking about the high output  

AZDesertDog:
ya. I got 4.10 front and back and both axles are locked. Im looking for power. Soooo back to asking about the high output

If you have a lift and big tires, a 4.10 is not a good gear to power it with a 6 plus a HO engine makes more HP at higher RPM's but makes no more HP or torque at lower RPM's. Short of a super charger (which will strain tranny, engine and cooling system) you are not going to see the torque boost needed to pull your gearing and tires with authority. Depending on current or planned tire size a 4.56 or 4.88 could be the game changer you are looking for. I might add the replacement locker are not wise up front because they add to stress on front axle and effect handling because both tires cannot be power in a turn with different rolling radius unless they are forced to skid and this take power to overcome and can make SUV feel weak at times.