I recently put 31/10.50/15 tires on my '99 toyota tacoma. These are bigger than the original size that came on the truck. Do I need to have to make any adjustments to the computer to adjust for the larger size?

no no, it should be fine. My cousin put 39.5/14.5 tires on his truck and everything was still the same. You should be fine, don't worry about it. :)

the computer will be fine and your fuel mapping will change accordingly..you might lose a little power..what gears came on your 99?

the only thing that will be different is your speedo might be a bit off...

i had 31' on my truck when i bought it...now i have 32's...the puter is off by about 1-2 mph...not a big deal....