SES Flashing, shifter shaking???

I posted a message earlier this week (attached below if you are interested). Well, I've been working 12 hour days since and haven't been able to fix the truck yet, but this morning, I got in to come to work, and the SES was flashing, and the shifter shaking really badly when I would step on the gas. I drove it around the neighborhood a few times to see what happened, and the light went solid instead of flashing, and the shifter stopped shaking. Does this sound like anything you've ever heard? People had suggested my problem could be many things, but the most common answer was fuel filter. Would that cause this??

My previous post:
A couple of weeks ago, my 99 Blazer 4x4 was taking longer to start. It would crank just fine, everything sounded like normal, but I would have to hold the key longer before it would actually start. It seemed to do it more after it had been sitting longer. If it had just been running, it would start up no problem. I brought it to the shop, and they told me it needed a fuel pump. They replaced the pump. I got it back and to my delight, it was working great, and replacing this fixed a couple of other problems I was having.

All of a sudden yesterday, after driving all day in hot weather, it was doing the same thing only this time, it seemed it just wouldn't start well if it was hot, but once the sun went down, it had no problems, even after a long drive (hour long). Any ideas what this could be??