it has cold air intake and a highflow muffler but the automatic-transmission slips out of gear occasionally. sometimes it feels sluggish on the freeway. and when put in reverse it grinds if im on a hill.

there is no metal shavings on the transmission dipstick yet what are the possible reasons for this? and what could i be looking at for costs.

also i would like to increase its performance yet i cant seem to find performance mods on the internet.
is it just the fact that my car is so old?  

You might need to replace the transmission filter and do a transmission flush to get rid of your slipping and other problems, if not finally know what's wrong with it...

High flow mufflers with the stock "coffee straw" piping might not do any good, but you could just go to a muffler shop and tell them to give you a bigger sized piping to fix your ills and keep the muffler (which I hope ain't a coffe can muffler).

There aren't much for performance, but I did find some stuff for the suspension.

You could get a set of 4 15X7 BBS RG-F forged wheels with a set of Dunlop Direzza Sport Z1 Star Spec Tires for about $2,000. (There are cheaper brand rims that are just as good like Enkei, Rota and others, but nothing says I'm wasting my money like Forged BBS Rims )

There is also a Tokico HP (Non-Adjustable) Performance Shocks/Springs Suspension Kit for about $400.

In all I'd recommend you take it to a reputable mechanics shop or cough up some dough at the nearest Honda Dealership and tell them to Flush the Transmission and Replace the Trans Filter, and do a complete tune up, which would change the Timing chain, belts, I think spark plugs, sparkplug wires (I don't know I rather do that myself), fuel filter, air filter, oil filter, and other stuff that I can't think of now.  Then get that nifty Wheel and Tire package and the Suspension upgrade and have some fun.
   

     Remember its your first car and It'll be yours for a long time (or until it busts) so don't be in a hurry and take your time, just take care of it for now and save up for all that stuff and have fun that's the most important thing, screw that A-hole who brings the 08 Shelvy to School, *** him! *** him sideways!!!!  

The transmission thing will run to about 150 at best...If it ain't broken....  

don't forget to clean the injection system.  

ya
to modify a car like that, youb might need to do a lot of custom modifications and the use of some ingenuity. I own a p.o.s. 89 Ford Tempo, and the only aftermerket thing I could buy for it would be a set of 15" alloy wheels with some nice rubber. That alone would improve the feel of teh car, but I know everyone on this site is thirsty for more power. As far as custom mods go, I've found some guys online who've put the 220hp Yamaha V6 from an SHO Ford Taurus into a Tempo. It look a lot of extensive modification, but it showed me that something can be done to my crappy lil car. In your case, and engine swap with a vtec civic or newer prelude might be an option. You can always customize and retrofit things in order to make them work!!