The TM-733 is not that old of a radio. They were in production in the late 1990's. While old capacitors could be the problem, that's not the first place I'd look on a modern solid-state mobile radio.
Check your power supply. The radio draws 10-15 amps at 13.8 volts when transmitting on high power. If the voltage from the power supply sags too low when a load is presented, the radio will respond by shutting down the transmitter or cycling the CPU (which would make the display reset).
Also check all of the connections between the power supply and the radio. If the inline fuses are still in place, the fuse holders may have picked up some corrosion which would cause a voltage drop at the radio. Same goes for the T-shaped power connector...make sure it's not corroded.
Best options for Kenwood service are the authorized Kenwood service centers listed on the Kenwood web site. The first two listings
here handle amateur radio repairs. Take note of the Out of Warranty Repair info at the top of the page. Cliff at
Avvid also does good work and may be able to help if Kenwood can't.