Desktop UA site and all reliable methods of pricing give the $376 / $352 numbers. Not sure what might be wrong with your app.
Suggest pricing economy on those same 2 flights (T) to LAS and (K) to IAH. Towards end of booking, you will be offered a buy-up to First. See if that price is less than what you would pay for the P fare now. You have 24 hrs to cancel & get refund.
I would use caution doing this - reports are that buying up during booking does not re-fare, and you miss out on extra PQM.