Engine Running Rough

I have a '94 blazer with over 153000 miles on itm it has a slight problem, or something, which concerns me: sometimes when I first start it up, it will run rough for a little while, and is significantly louder, after I start driving a little ways, it usually smoothes out and runs fine. However today I had a 20 mile trip, traveling most of the way at 55 mph, and it was still running rough like this at the end of the trip. It also seems to be doing this more frequently, there are no lights or anything else unusual. Could it be the EGR valve? Or one of the sensors? Any help or thoughts would be appreciated!

Like the question I posted earlier about my suspension its hard to give any suggestions without being there to see it, in your case I don't think it would be a sensor, or the EGR Valve because something like that would cause the engine light to come on. You may want to check your plugs but again if it was misfiring that would cause your engine light to come on. Check things like filters, fuel/air/pcv/ ect. may want to check IAC sensor for sticking and for ****s and giggles pull off egr valve and try to clean any carbon build up (can't hurt) but that's just my 2 cents.

Run higher octane, change plugs/wires, clean the EGR Valve, and see if that clears it up.

Thanks! It is almost consitantly happening now when I start up, and it will sometimes "go away" and sometimes it won't. After hearing it more, I don't no that I'd say it's running rough as it is "louder", it is kind of rough, but mainly"louder" - that's the best way I can describe it. It also ran hotter yesterday - 240-250 I'd say. Is that related to my problem, or just because it was 100 outside and I was running the A/C? Again, thanks for all the help!