The open/closed loop is almost certainly not what the problem is. Even if the TPS was not sending a WOT signal, the fuel maps are not allowed to go into closed loop over 4k(?) or with any decent airflow.

My theory is that your knock sensor is going crazy, which is forcing the ECU to pull timing way back. That would make it feel like gutless. There is an enrichment table in the ECU versus coolant temp, but it only takes about 1-2 minutes to get to the part where it's basically no correction. Anything past that will not be coolant temp related.