2006 Ford F-150 Engine

Hey guys I was going to see if someone could give me some insight about my 06' f150 fx4 (140k miles). Here's some brief history about it: I purchased it used and it ran fine for a while but the dealership I got it from informed me that it was "missing" or kind of sputtering when you get it up to about 45 mph but if you give it a little gas then it would stop. This went on for several months (occasionally) but then it started to get worse. One day I was getting on the interstate and while I was still on the on ramp, it started "sputtering" around 45 mph and as I started to accelerate, the truck started to feel like it was shaking and it almost sounded like it was stuck in a low gear. Needless to say I felt like I was riding down the interstate with my truck in first gear. I took it to the shop in town and they ran some test saying that a few of my coil packs needed to be replaced and that was it. After they replaced the coil packs the truck ran fine for several months but it started to "sputter" around 45 mph again so I took it back to the shop and after they ran some test and scratched their heads for a while, they came to the conclusion that my computer needed to be replaced. They finally got the computer replaced and the truck ran great for about a year and half but then the "sputtering" slowly started happening again so instead of taking it to the shop in town, I decided to take it to the ford dealership cause I figured they would know the problem but of course they said "everything looks fine but a few coil packs are going bad." So I had them replace the coil packs (this was a little over a year ago) and they sent me on my way. Within this past year my truck ran great but earlier this week (2/09/2014) my truck started acting up again. I noticed when I would crank it, it seemed like it was idling pretty high and it started to act like it wanted to "sputter" around 45 mph again. (We've had some cold weather these past few days (sleet/snow) and since I live in the south, I wasn't sure if low temps would effect my truck's performance so I didn't worry too much about it at the time.) So here's what I'm dealing with now: when I crank my truck it idols abnormally high and whenever I put it in drive and start driving, I noticed a loud rattling noise coming from my engine ( something I haven't noticed before in the past) whenever I accelerate and also when I decelerate. This rattling noise is loud enough to be heard over the radio so it has me worried. And of course when I get up to 45 mph my truck starts to "sputter" intensely, almost like its stuck between gears and my truck acts like it doesn't want to go any faster.

If anyone has any idea of what might be going on I would really appreciate it! FYI I keep my truck up to date on everything so it's not like it's been neglected on check ups. I know I'm ultimately going to need to take it to the dealership but I was going to see if anyone had any info/advice.

Thanks,
Joseph