Could be a clogged PCV valve (jiggle it, can you hear something rattling?) or could be bad piston rings causing blow by.

Here's another post just the other day with similar problems

http://www.4x4wire.com/forums/showf...mp;amp;sb=5&o=14&fpart=1


88 4R, 350 V8, R150 5 speed Sold <...uot; />
97 4R, stock, daily driver
98 Sienna, kid and dog hauler, wife's ride