I don't use the X-Sim Play button, because I am a bit too much of a control-freak to leave things entirely up to my coaches, but, depending on the quality of my underlings, I sometimes rely heavily on Ask the Coach. When you've got a top OC/DC with 5 playcalling, its not the worst of ideas, although I still veto a decent amount of calls. There are other franchises in which I pretty much exclusively call the plays - it depends.
One reason your running game might be suffering is that you don't get the heads-up notification of your running back's fatigue hitting dangerous levels that you do in-game. And the more tired the back is, the less effective he will be. To check fatigue levels and sub in and out, use the Injury Report screen off the start menu. Even in pass-heavy franchises, I usually have to do some subbing, but in run-heavy franchises I've had 3 or 4 back rotations to keep everyone fresh.
Firing a 91 trainer's not good, but if it was after year one, you're still alright as Arron Lee (99 OVR) will pop up every year after year one. If you have to settle for a lesser trainer, well, then I hope you're up for a challenge
