I know it need major maintenance?

Nice truck! That is a good start. I would do an engine tune up and flush out the brake fluid for fresh. Also, a differential service would be a good idea as well. Here are three guides will the instructions below to help as well. Also, check the transmission fluid condition and if burnt I would change it out as well.

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

and

https://www.2carpros.com/articles/how-to-tune-up-a-car-engine

Here is a guide to help you service the throttle bore and IAC motor as well:

https://www.2carpros.com/articles/throttle-actuator-service

Here is how to service the differential:

https://www.2carpros.com/articles/differential-service

NOTE:
Be sure to note routing of secondary ignition cables. Failure to route cables properly may result in radio interference, ignition cross fire, or ignition short to ground.

REMOVAL

1. Spray compressed air around spark plug to prevent foreign material from entering combustion chamber.
2. Remove spark plug wire by grasping boot and turning 1/2 turn while pulling boot back in a steady motion.
3. Remove spark plug using socket with foam insert.

INSPECTION

Inspect plug for:

1. Cracked or damaged threads or insulator
2. Worn or bent electrodes
3. Damaged gasket
4. Electrode wear or excessive carbon deposits

INSTALLATION

1. Start plug in cylinder head by hand to prevent cross threading.
2. Torque spark plugs to 30 lb-ft (41 Nm).
3. Install secondary ignition cables on spark plugs, (be sure connectors are pushed onto plug completely).

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