It appears that all Montana Mountaineer's used 235/80R16E tires and they need to be set at 80 PSI cold. I don't know if 5 lbs too low will cause all the problems you had since other variables come in to play as well such as your traveling speed, how heavy you were and what the ambient temperature was. But the biggest contributor was simply you were running ST tires. They are just flat unreliable when used on the heavier 5th wheels. We changed from the OEM Chinese made 16" ST Tires on out Montana 3400RL to 16" Bridgestone R250 Duravis LT tires and have not had trouble since. They will run around $200 each. I believe the Maxxis ST Tiresare quite a bit more expensive. I will never install another ST tire on a 5th wheel or trailer.