TPS54560 in thermal shutdown at 4 Amp load

I am using a TSP54560 step down regulator in an automotive application, input range 9v to 55v, output 5v and 4 Amps. At full load (4 Amps) the regulator transistor switch is disabled on a 2 second interval. This appears to be thermal shutdown as it takes awhile to show up and spraying either the regulator itself or the catch diode with circuit cooler will bring it back to full operation for a period of time until it heats up again. Efficiency is measured at 67% with a 9 volt input which seems a bit low, 77% on a 24 volt input. Data sheet shows 85% efficiency at 12v input and 5v output so I was expecting better then 77%. Switching frequency is 330 KHz and inductor is 22uH. I tried increasing the switching frequency to 660 KHz to lower the ripple current in hopes that would increase the efficiency. All that did was increase the on/off rate to a 1 second interval. I also tried changing from the electrolytic cap 220uf (ESR not that good) to 2 100uf ceramics with low ESR, again no change. Trying to figure out why my efficiency is so poor, fix that and the thermal problem should to away.  I am not getting anywhere close to the efficiency shown in the data sheet. Any ideas why that would be? One note, measured efficiency is end to end and I have a load dump transient protection circuit on the front end and 2 TPS2511 USB port controllers on the output end with load switches all of which contribute to the efficiency. Still the TPS5460  is getting hot enough to go into thermal shutdown which is not what I am looking for.