So, ... How old is the JC and what model? Regardless, here are some easy places to start looking: When I had similar issues, the fuel systems were restricted. Could your fuel filter need cleaning? RXi's have filter in the turbine. RXi filters are small and very fine. Could a fuel line be pinched? Could debris from inside the fuel tank be plugging the clunk? (I once had a piece of glue from inside the tank break loose and plug the clunk.) Is the fuel tank vent plugged? If the UAT is compressing at WOT, then there is a restriction in fuel to the UAT. If all of the above are O.K., then I would be looking at fuel pump voltage? Hopefully you have some pump voltage baselines recorded to compare the current reading to past readings at Idle and WOT.