What's wrong ?

Only bought this 1996 Civic LX because the price was right and was owned since new by a friend of my wife's ; never hurt , never abused. Now I've become a fan!
Terrific car, not too powerful but nimble to drive and oh so economical.
But....it seems to be having some transmission (4-sp.auto) problems. Shifts hard especially when cold. Late, hard shift from 2nd - 3rd when cold. More bothersome is an intermitant refusal to go into 4rth gear lock-up. Sometimes works perfectly;
sometimes just refused to enter lock-up.
Flushed tranny and replaced fluid with synthetic. Big improvment but still occassional refusal to enter lock-up at highway speeds. If "backing off" going down a hill it properly drops out of lock-up but is very stubborn in locking back up. Funny, if I put the brake on to take it out of lock-up fist, it will jump back in with no problems.
I've been told it's the linear solenoid. I've been told it's the lock-up solenoid ; the
engine load module ; all of the above and none of the above(just keep flushing till all passages are clear).
Anyone run into this problem or have any idea on a fix? Any help and/or ideas would be appreciated.