Toyota W58 5spd manual pops out of 2nd under med-high load

i there, I have a 5 spd manual that works fine except 2nd pops out so often I hardly
use it and skip to 3rd which really suck since I have a nicely modified 1600 motor in
front of it I like to drive a little harder now and then when Im mucking about outside
town -

This is a ford Kent with a toyota trans adapted to fit - so I just chose a toyota celica. I
believe these came with a W58 but I could be wrong with yr / etc.

I must add my gear lever bushing is toast, I need to replace the large female one that
sits in the transmission. Ive tried all kinds of hacks but nothing lasts, it just gets eaten
down there.

I also drained and filled the trans with a Castrol glx-4 trans oil which the trans calls for.