Maintance I have 190,000 miles on my toyota tacoma prerunner (4cyc. 2.7 liter) and the only thing i have changed is the oil,and spark plugs. This truck has never seen a shop before i have no problems but my question is should i start replaceing anything inside the engine before it breaks?

Obtain a Hayne's Repair Manual. They go over spark plug replacement.

Time string? Do you mean the timing belt? 100-140 miles is a good rule of thumb. Definitely have a pro do it though, things can get tricky on a truck that new.

a safe bet is 3000miles or every three months, whichever comes first

smells to a wrong spark plug type, double check your numbers, if doubt call your locall toyota dealer parts department. Toyota vehicles are very sentimental about originall equipment plugs, dont like aftermarket plugs, also check your air filter housing and make shure all hoses are atached.
Good luck

2001 Toyota Tacoma Prerunner, 3.4L, 4 door, 2WD, automatic transmission overdrive problem. It's not shifting to overdrive, overdrive button on shifter does not turn light on - on dash. Mileage is 115,xxx.

2000 TOYOTA TACOMA 2.7L 4-cyl Engine Code 3RZ-FE

Engine Oil Grade 1......API* All TEMPS......5W-30 Optional ..10W-30
Engine, 2WD, with filter..........5.5 liters
Engine, 4WD, with filter..........5.4 liters

Manual Transmission,......GL-5/ GL-4 All TEMPS......75W-90
Automatic Transmission,A340E......AF3 / A43D......AF3

Differential, Front/ Rear W/ ADRD......GL-5 ALL TEMPS......75W-90
Differential, Front Less ADRD......GL-5 ALL TEMPS......80W-90

Transfer Case,......GL-4/GL-5 ALL TEMPS......75W-90 Gear oil.

Capacity:
Cooling System, Initial Fill..........8.5 liters
Automatic Transmission, A340E Initial Fill..........1.6 liters
Automatic Transmission, A340F Initial Fill..........2 liters
Automatic Transmission, A43D Initial Fill..........2.4 liters
Automatic Transmission, Total Fill
4 speed A340E..........7.2 liters
4 speed A340F..........10.1 liters
4 speed A43D..........6.5 liters
Manual Transmission, ..........2.5 liters
Differential, With ADRD Front..........1.2 liters
Differential, Without ADRD Front..........1.1 liters
Differential, 2WD V6 Rear..........2.6 liters
Differential, 4WD Extra Long Rear..........2.5 liters
Differential, Short WB With LSD Rear..........2.7 liters
Differential, Short WB Without LS Rear..........2.6 liters
Transfer Case, Electronic..........1.2 liters
Transfer Case, STD..........1 liters

Start with the plug wires.You may need new plugs but my experiance is that the plug wires are the first to go.

It's probably not the fuel filter. I would suggest replacement sparkplugs, and wires, since you did not nmention these items. Also, use plugs from a Toyota parts dept. If you use anything else, it won't run properly.

Usually this is a bit of dirt in the engine plugging the oil port that supplies pressure to the variable valve timing control cam. Change your engine oil every 3000 miles and maybe switch brands. I had this problem on my Matrix until I switched to Castrol GTX 5W30 that cleaned the oil port right out.

My truck did the same thing. I changed the plugs with the ones the parts store recommended and it still acted gutless. Then I took it to the toyota dealership and they told me the plugs were not the right ones. So make sure you have the right plugs with a couple different parts store. i guess there sensitive and not just any plugs will work. Do it yourself though cause the dealership will rape you. Stevenson toyota in Golden colorado sucks!