[xdalaw]

Do you have other programs running in the background that you thought you already closed?
I have little trouble multi-tasking with the Pro, and the OS should even close programs if you're running too low on memory to run them, but it's hard to know exactly what's going on without more information.
Have you soft-reset your phone to allow it to clean itself up from misbehaving apps? (I have an app set to soft-reset my phone automatically each morning before I start the day.)
Are you using the stock Sprint ROM? Have you tried a custom 6.5 ROM? (It might have better built-in memory management.)
Good luck.