For the USDM sr5 and gts were there zenki and kouki years? Or is that a JDM only thing? Thanks.

Both JDM and USDM cars had zenki and kouki years.

For USDM cars, here's the breakdown:
-1984: Only SR5 model were available (zenki)
-1985: Both SR5 and GTS models were available (zenki)
-1986: Both SR5 and GTS models were available (kouki)
-1987: Both SR5 and GTS models were available (kouki)

USDM GTS cars (from zenki -> kouki) got slightly beefier rear axels, updated bumpers + trim, different side graphics, different interior (door panels), updated tail light design. The engines stayed the same.

There's lots more to it than this, but there are the basics. Google around a bit for some more comprehensive guides.

Thank you for that information!

Ryeguy, I hope you know that the terms Zenki and Kouki are Japanese words meaning (in this context of cars) earlier term or before minor change and later term or after minor change, respectively. Hence you could use those terms on ANY car not just an 86.

in terms of additional differences, obviously a different Diff to compensate for the larger/thicker Kouki axles, the clutch master cylinder is also slightly longer in the Kouki models with a bushing to reduce the noise commonly found on a Zenki CMC.