My 2002 mustang GT has over 110,000 miles. I need to do a full tune-up/service. What is recommend, I have only changed the oil (every 3k miles) and changed the belt since I purchased the car new.

Have you checked the rings around the cylinders? That might be it.

Unless you know you have a 100,000 mile motor specifically I always recommend full tune ups at 50,000. that being a tune up includes plugs, wires, pcv valve, inspection of all brake pads and shoes and a full lubrication. Oil and Filter changes at 3000 mile intervals even with synthetic oils.

At this interval it would be a good idea to check your drive belts, coolant hoses, motor mounts, suspension bushings, check for any motor oil leaks which could occur from any leaking gaskets. It is also a good idea to have change your spark plugs at this point as well. Normal spark plugs last around 50k miles before there electrodes start wearing out and losing their heat index value. They may still be functioning but at the cost of a lower grade spark and less than optimal fuel economy. If you've never replaced your power steering, brake, and transmission fluid and filter now would be a good time. I'd recommend replacing with synthetic grade fluids. I'd also recommend changing your motor oil on any vehicle every 2500-3k miles and adding a quality motor oil like castrol or valvoline, I personally use and recommend stp oil treatment, 1 bottle added at every oil change as well as marvel mystery oil in both my motor oil and added to my gas tank, this is remarkable stuff which keeps the internal components of your engine and fuel injection system clear of residual build ups. Be sure to also check and replace if necessary your air filter as well. good luck and hope it lasts another 90k miles for you

New spark plugs, oil and oil filter, transmission flush and fill, fuel filter, air filter, coolant flush and fill, clean throttle body plate and bore, clean the MAF sensor, replace any loose or cracked vacuum lines, PCV valve, new air filter, new battery.

99% of the time all you should ever need for a tune up is new spark plugs, and a clean air filter and throttle body. But since your inquiry indicated "major" I gave it more critical thought.

don't know about the MPG it could be a lot of things. I have a 2001 Jetta TDI. You should NEVER change the oil at 3K miles. VW recommends 10K miles for a reason. The Synthetic oil has additives to remove varnish and it does that but it needs some time to replace the varnish and properly protect sensitive engine parts. 3K is oil changes are not a good thing for a TDI......Just use the right oil and change at 10K

Yes it is. On your newer vehicles the factory has set your oil change light to come on at 5k, due to the technology in semi synthetic oils. Mazda uses a semi senthetic oil from the factory. I still recommend changing your oil every 3k. You may also consult your owners manual for the recommended service interval and adhere to it. As long as you adhere to manufacturer recommendations and keep your oil change reciepts, you should be ok if anything were to happen.

A tune up for your engine should be done at 100,000 miles, the factory plugs are designed to last that long before changing. The oil and filter and air filter should go by the maintenance schedule in your owners manual.

well its always recommended every 3000 miles to change the oil if you are using mobil1 full synthetic oil then every 5000 miles transmission i recommend every 45000 miles 60000 mile should be radiator fluid,power steering,fuel filter if trans hasnt been done then transmission

One thing to check is if the fuel pump is working and what the fuel pressure is. The pump is inside the fuel tank. The pressure must be 35 to 65 psi. The pump can be working but if the pressure is not enough the car will not start.