Difficulty with Touchscreen

[PaulF]

I have made quite a few successful circuits with TFT touchscreens, however I am having great difficulty getting a touchscreen to work on a new board.
I am using a PIC18F47K40.
The display works fine and I have tried everything I can think of however the touchscreen refuses to work.
I have a similar board with a PIC18F67K22 & the same touchscreen with the same Firmware (with corresponding config etc for the PIC) works fine on that. The only other difference between the boards is the PIC18F67K22 is using an external oscillator but the PIC18F47K40 uses internal.
I have monitored all the touchscreen pins on a scope & everything looks identical on both when the screen is touched, with the exception of the T_DO(MISO) pin on the PIC18F47K40 which is permanently low.
The simple program with only the display and touchscreen gives a readout on the display when the T_IRQ is detected, to show wTftTouchX, Y & Z from "TftTouchScreenReadValues() which remain 0 (with the exception of Z which is 0289) on the PIC18F47K40 board, but change with each touch on the other board.
The touchscreen pins are all on their own micro pins & I have tried on different ports etc which don't have PPS just in case that was the issue & have checked all connections etc but the problem still persists.

I am almost at the point of admitting defeat with this particular micro but maybe I can't see the wood for the trees, can anyone who understands how this all works better that me, give me any pointers as to where to look?