RE: holding first gear?
Ding Ding Ding!!!
Absolutely correct!!!
No matter how much you want to grenade your engine or balloon your torque convertor, the PCM will not allow the transmission to remain in Manual First.
Based primarily upon information from CKP(Engine RPM), ECT(Coolant Temperature), TFT(Trans Fluid Temperature),and OSS(Output Shaft Speed), if the PCM believes catastrophic component failure is imminent and the driver is too dimwitted to get the transmission out of Manual First, the PCM protects his car and forces 2nd Gear.
If he's really hell-bent on breaking something and manually pulls First Gear at higher speeds, the PCM will not allow the downshift until 28-30MPH or a safe RPM window.
Why would you want to do this?
What possible benefit is there in holding First after the PCM has decided it's dangerous?