Car Behaving strange

[jared_drivebird]

I have a 1994 3.4 and its been behaving strange. About three months ago I had an issue where once a week to maybe 3 times a week the car would at 45 to 65 mph suddenly start cutting out, best described as if the engine was being starved of fuel. Would only do it for a second and then it drove perfect. I woke up one morning and took it out and it was just full blown..it did it all the time at those speeds and only at those speeds.Then if I floored it the car would just accelerate fine. sometimes it would slightly "backfire" when I did floor it when it was doing that. If I drove the car for about 40 minutes at those speeds it would eventually stop for the most part. I tried checking several things and didnt have the time or the patience for what might be wrong. I took it to the shop and had a tune up. They changed fuel filter, plugs, cleaned injectors, ect.... Drove it out that day and it drove flawless. 2 months later (now) its starting to do it for only a few seconds once a week just like it did before. Only this time when I start the car after its been sitting for a while ( 6 to 7 hours ) its starts fine but the engine is missing, I can hear when I start it and when I rev it in park. As soon as I put it into gear it doesnt miss anymore and runs perfect. Any explination for this behavior? anyone else had this problem or similar. Any help would be excellent!