Viscosity goes down when the oil temperature goes up. Most people guess that they need thicker oil because... well, because. So before changing viscosity grade, have you accurately measured the oil temperatures under the highest load, worst cooling condition? And under those conditions, what was the oil pressure? Gen 1/2 cars didn't have oil temperature gauges and have a so-so electric pressure gauge. Coolant temperature is not a good substitute because the oil has it's own heat exchanger and thermostat. In my car the coolant temp goes high in city traffic but oil temp stays normal. On the track the coolant is a little high, but the oil is much higher. You should measure this. If the pressure is less than you think it should be, move up a viscosity grade, although testing I've seen shows that the viscosity grade will only add a handful of PSI; If you really want higher pressure, keep the oil cooler. However, at some point the pressure relief valve will dump it anyway. Oil pressure will not cure an oil pick up problem in long high G turns.
I suspect SRT uses the 15W50 because it is extra extra extra extra insurance against the oil running hot. Even NASCAR uses lower grades and Mobil sells a Racing 0W30 that Penske uses. I wouldn't assume any oil is "too" thin (Formula 1 uses 0W20, HEMI comes with 5W20, some NASCAR team use a 0W20, Champ Car when alive used a 0W20, almost all Fords and Hondas come with 5W20) these days. So there is nothing wrong with the 10W30; the 0W40 that Dodge now recommends is simply the newer year model version of engine oil.
