it sounds like you have the wrong driveshaft maybe try a diffrent driveshaft setup to fix that problem dont compromise your trannys your going backward not forward.
do not go w-58 with a 1JZ the 1j is factory 280hp and the 7mgte doesnt even use the w-58 and it is 230hp. the w-58 threshold is no more then 300hp period and the 230hp 2jzge n/a has been known to break the manuels and there is verry little diffrence between the mkiv w-58 & the mkiii mainly it was the synchros or something verry little and there was a slight diffrence in the number of parts or ribs on something i cant remember.
you can use R-154 with 1JZ
you can use V-160 with 1JZ with moded final gear
you can use V-161 with 1JZ with moded final gear
you can use T-56 or ZF6 or there is some american 6 speeds high horse you can use with it using some custom parts because i have heard of kits to fit american transmissions with the 1000+ hp 2jzs esentialy the same as a 1JZ that may even open up some sequentials you can use that are like almost 10,000 for the mkiv and maybe a richmond or some other tranny after market here you go i found what you need below
omg i just did a search on summit for some of there 6 speeds go here they sell a direct kit to bolt on any american tranny to a w58 which is for only $419
http://store.summitracing.com/egnsearch.asp?N=700+115+317551&D=317551
& get this tranny you will be set! you can goto 600hp+ or so with these manuels.
http://store.summitracing.com/partd...908216+4294925134+4294839071+115&autoview=sku
oops this bellhousing is to put an LS1 to your w-56 but why well find the one that mates your 1-2jz to a richmond and your set i know they are out there.
