OK, here's my situation:

I have a '99 V6 with 118K miles on it and I'm trying to decide if I can cost effectively improve the handling a power to get is closer to what it was like when it was new, or if it's just more cost effective to just buy a new Stang.

My two issues are:

1-The suspension has gotten sloppy and it feels like the rear end shifts around too much when I take a hard turn or hit a bump. The dealership didn't find anything wrong with it, except that it could probably use a new tie rod.

2-The car just isn't as quick or fast as it once was and I've even upgraded the final drive gears to 3.73's. I'm not sure if this is simply because of the age of the engine, or if a "tune up" could help get most of the power back.

I was kind of wondering if a "tune up" along with some sub frame connectors and new bushings would do the trick.

If anyone has some input, I'd definitely appreciate it.

 

All the stock bushings in the suspension are made of soft rubber, which can deform and decompose a bit over time, hurting performance. I replaced the bushings in my steering rack with urethayne ones, and it did help a bit. Unfortunately the cost and effort in replacing all of them would be pretty overwhelming.
A better bet would be to replace indivitual items like control arms, springs, and sway bars with higher performance versions. It'll be a much better investment of your time and money.

The engine performance can deteriorate some over time, but it's possible that you're just more used to the acceleration now and it's not as thrilling as when you first got your car. I'm less impressed with my car's performance now then when I got it, despite the fact that it is quite a bit quicker now. It's possible that your pistons or cylinders have some scratches and your compression has dropped, particularly if the oil wasnt changed as regularly as it should have been. That would certainly hurt the power output, but you would need a compression tester to check for sure.
A 'tune-up' might find a problem, but it could also be a big waste of money if you spend a couple hundred dollars for new spark plugs, coils, filters, etc., and none of those are the problems. If you have a trusted mechanic friend, you should talk to them about it.

 

Thanks Mudshuvel. I appreciate the tip on the bushings. I know what you mean about getting used to the acceleration, unfortunately I can tell it is more than just that, because it just doesn't seem to get up an go compared to even some less performance oriented cars. However, a large portion of it may be a result of losing power through the soft suspension.

I definitely need to find a good mechanic and there should be plenty here in the Motor City, but I just moved here a few months ago, so I'll have to do some asking around.

 

Glad to help. Hopefully you can figure out why your engine performance has dropped, but it's pretty tough to diagnose the problem online.