We can try to measure this but the more I'm driving this the more I can "feel" the symptoms pointing to TPS and this puts it on the to-do list.The TPS was a weak spot on the EEC-IV cars, it would develop a flat spot, which can cause exactly what you are experiencing. If you have a good multimeter (preferably with an analog sweep) you can watch it, it should be very smooth from around 0.9V right up to 5V (WOT). If it does some weird jump or dip, it needs a TPS. The 351W (EEC-IV GT-40) in our boat needed a TPS for this reason.
They describe TPS adjustment in numerous sites but for my eyes the holes on TPS allow no adjustment. Perhaps it is for older models.