What can i put in my 2003 tacoma 4 cyl. diffs to lock them?..And what size are my diffs?

See my response to your other question. A Toyota dealer should be able to give you some options and may even have a Toyota-recommended differential locker available to you.

You can do a lockright, Aussie, Detroit, ARB..... Lockrites and Aussies are lunchbox lockers. You just replace the spider gears with them. Detroit is a whole unit that you swap in. ARB is a full on air locker. You could also swap out a whole housing, 3rd member and axles for a trd rear end, and get all the electronics, but then you have a SLIGHTLY weaker rear end. Your rear end is a 8.4" Non-TRD rear end.

Do you even own a Tacoma???

125,000 MILES ON A LOCK-RIGHT In March of 1998 I installed a PowerTrax Lock-Right model number 1611 into a 1997 2WD Tacoma (2.4 liter engine). The Lock-Right was installed to provide improved pulling power while living in the Colorado mountains instead of taking a loss by trading in the truck for a 4WD. The cost of the Lock-Right was approximately $250. This 2WD Tacoma with the Lock-Right kept up with the 4WD vehicles until the snow levels was too high for the lower ground clearance of the 2WD. There was approximately 32,000 miles on the Tacoma at the time of installation. In April of 2010 the Tacoma has 157,000 miles on it with the Lock-Right continuing to perform flawlessly for these 125,000 miles. The vast majority of the miles has been on highways driving across the country or in cities (New York, Seattle, Denver), and for a while the truck sat unused. The Tacoma is now in Alaska doing a great job pulling and launching an 18-foot skiff. Besides traction improvement the fuel economy improved a little with the Lock-Right. The clunk-clunk-clunk sound continues as the vehicle goes around corners, with no apparent change in the sound over the years.