I do know that very very consistently I will get a buy filled at ETrade with the best price even if my limit price was higher than the current price with the intention of buying a lot more shares than available at the ask.
They will buy highest ask price that is < $5.50 or = $5.50 . If you set limit at $5.50 highest ask is $4.50, you will get shares at $4.50. At least, that's what I have seen in Ameritrade.
I have USAA and E-Trade Pro. I've been with USAA for over 20 years. Switch to E-Trade as soon as possible for all OTC trades.
USAA will not allow Stop Loss Limit on any OTC trades.
Don't use Market Price. Ever.
If you have PM, I'll talk you through all of my experiences with both and why you should switch for OTC trades.
In the meantime, when you go to USAA, set your limit price for about 5 cents over what they show as current share price (They are real time on quotes) and buy. They will give you the best price at the moment you hit place purchase.