1995 mustang problem

I have been bashing my head trying to figure out what is wrong with my car i just bought. i just bought a 1995 mustang convertible with only 24,000 miles on it. The problem I have been having is my car will randomley start shaking/shimmeing. It usually only lasts a couple seconds and as soon as i give it some hard gas it goes away. I took it to the ford place i bought it from and they flushed the transmission and it stopped shaking about 95% of the time but then about 2 weeks later it started coming back and now its doing it more and more frequently again. Any suggestions? Im starting to think the ford place just doesnt want to admit whats wrong because they will have to fix it for free. I dont know if this might be useful to know but it occurs most frequently at certain spots. for example right outside my devolopment it occurs almost everytime i leave my house at this certain spot. I dunno why it would do this. I mean it doesnt happen all that often but its just really annoying when your driving and it starts shaking and then you have to give it gas to make it stop shaking. It occurs usually between certain speeds which are 25-40 mph. Any suggestions would be greatly appriacated. thanks.

does it shake when its idleing too or just at speed cuz if it only does it when ur going 25-40 u might have a bad u-joint and the only good way to check is to take the both off and look at them if they look like their warped or dicolered than it might just be a u-joint. it may also be the harmonic balancer my car had the same problem the rubber in the middle can slip back and forth hence why it only does it some times. by the way is it a 5.0 or v6

It is a 3.8L V6.. No it hasnt happend yet when i have just been idleing. I already had the U-Joints checked and it wasnt that. Now what was the other thing you were talking about that you had the problem with? Thanks

I already had the U-Joints checked and it wasnt that. Now what was the other thing you were talking about that you had the problem with? Thanks

the harmonic balancer is basicly the main pulley on the front of the engine on the crank, its a round weight with a strip of rubber between the actual wieght and the center and the rubber can dry and crack and then portions can fall out and cause it to slip just look at it and if theres ruber stickin out or if u can manage to see if theres a gap in between then thats whats wrong and its fairly easy to change if u have the tools. if u havent done so already check ur wheels a wieght may have fallen off it could be that simple. good luck man, if u have questions still, keep them up i know im bad at explaining stuff.:icon16: