These vehicles have a problem with the end-clutch prematurely wearing out on the transmission causing a similar problem. You will need to take the vehicle to a Mitsubishi dealer to have a switch box and pressure guage installed to isolate the problem, if it turns out to be the end-clutch, there are updated parts to resolve this problem that are only offered through the dealer.
Technician
ASE Cert, AS Degree in Automotive Diagnostics