bogging out at 2000rpms

hello I have a 1998 toyota 4runner v6 sr5 with 193,00kms, I am stumped and can't figure it out when I am driving I get up to 2000 rmps i it just starts bogging and wont hit any gear, when i stay under that it drives beautifully, i have changed spark plug and wires checked the fuel filter, the throttle position sensor and check all tubing for leaks, i can't figure it out anyone have any ideas please

hi there, mine was diong the same problem were mine goes to 3,000 RPM and it revs. back to 1k rpm and will not change gear as you mention, so after months of figuring what is causing it and finally I figure it is the computer (ECM) is toarst, and very expensive but junk yard sale it around $200 pr you can try ebay.