2001 Accord V6 LX Transmission Won't Shift

I have an 01 Honda Accord 3.0 V6 LX Coupe which
I bought well used (and as is with automatic
transmission and air conditioning problems) with
215,000 miles on it. The transmission after
warming up, slips out of 2nd and into 3rd with a
noticeable jerk and more often than not when
trying to drive at freeway speeds (60 -70 mph)
won't shift into 4th. I tried every type of variation of
acceleration to coax it into fourth because I don't
want to drive on the freeway continuously at 4000
plus rpm's. (Not to mention the gas mileage.)  But
to no avail until out of desperation at about 4500
rpm and 65 mph I quickly turned the ignition key
off then on again and voíla... It smoothly shifted
into fourth. I drove home from work at this speed
for 45 minutes. But when I exited the freeway,
came to a stop at a red light and tried to proceed, it
was stuck in 3rd or fourth and accelerated very
slowly... So I downshifted manually to second
which did the trick. Any suggestions? (Besides
getting rid of it) I paid very little for it but love the
strong V6 V-Tec motor and want to keep it.