stumble

Well after hours and hours of following guides and videos and blah blah blah.. I finally found the issue of idle surge, hesitation under throttle, stumbling, bad mileage.. etc. Incorrect spark plug gap.. and since people are going to ask they were gaped at .035 not .055 and here is the reason...

have a 99 by 4.6! First off when I start it it jumps to about 1500rpm then creeps down to 1000 and just hangs there. I put a new iac on and nothing. Second, while I'm driving around 40 mph my card starts vibrating I can feel it in the dash almost like its shuddering. If I floor it, I wants to go...