I say wait until, at least, 5000 miles.
I just changed my new 2003 Tacoma (2.7L I4) engine oil over to synthetic, 5w-30 Mobil 1, at 5000 miles. I did the first change on the engine at 1000 miles, then again at 3000, before changing again, and switching over to synthetic, at 5000 miles.
I also changed my entire powertrain, front & rear differientals, 5 speed transmission, and transfer case. I used Mobil 1 synthetic gear oil in my transmission and rear differential, and Castrol dino in my front differential and transfer case. The front differential and transfer case only have an estimated 100 miles on them, so I'll wait till next year w/them before going synthetic, to allow more break in on them.
Boy my transmission and rear differential oils were dirty. The oil was a gray metalic color. I'm glad I changed them.
By the way, don't go cheap w/the oil filter.
[ September 08, 2003, 09:44 PM: Message edited by: GoHack ]