99 mitsubishi eclipse installed new clutch kit,all gears work except reverse,why wont it get reverse?

sounds like your shifter linkage in the trans is out of its gates and in reverse, if you pull off the shifter cover make sure all shift rod in the trans are in the neutral position then reinstal shift cover

did you put clutch plate in facing correct direction

Sounds possible you have the friction plate in backwards and there is no clearance. Retrace your steps and check the clutch operating mechanism, then any gear linkage. With the clutch centre plate, the raised part of the spring carrier is usually facing outwards toward the pressure plate fingers.

I don't suppose to know Mitsubishi cars at all but it sounds like a safety interlock related to the clutch pedal mechanism hasn't been reconnected correctly or may have been adjusted out of tolerance during the remove and replace process.

It is not the TCM, it is a failed transmission.

sounds like the clutch is "dragging", could be adjustment if cable clutch, or leaking slave cylinder on hydraulic clutch, or the clutch it's self, normally first gear would be a little tight to engage too

if it wasnt doing that before then yes i would take it back to the shop could be simple adjusment, or a broken switch,

transmission is gone

Your shifter cables have gona bad, i had the same problem and its not your clutch thats causing the problem. Your shifter cables are just worn out and you need to replace them