Shifting problems

93 Chevy 1500 2wd

So whats the actual solution? Conducting
many process of eliminations here.
My problem is:  when driving, my truck is
revving pretty heavily as it is about to shift
into 3rd gear. I took her on the highway to
test her out and every time shes about to get
right at 40 mph (keep in mind the heavy
revving) she doesnt want to shift into the
next gear even though her rpms are at the
max 5000. She then stutters a bit until i let
off the gas pedal and when down shifting,
shes pretty harsh. I just purchased her last
friday may 27 2016. I bought her not able to
drive her because her rear end gears were
messed up because her previous owner was
abusive and rode her through the mud. Ive
cured that ailment by replacing the pinion
and gears within the housing. THEN i was
able to drive her and discover this problem.
So, i replaced the transmission fluid after
opening up the pan and saw that nothing
within the transmission was fried. Nor was it
destroyed in anyway. So we ruled out
transmission needing to be replaced. After
the fluid change, she was handling a little
better. Then came the transmission mount
and motor mount. Today, i drove her home
and discovered the problem at 40 mph. Im
guessing by everyone elses problems here
that this is a common malfunction, and
taking an educated guess, id say theres
faulty wiring here and since some people
have changed out sensors and others have
replaced computers, im hoping im safe to
predict that mine and my chevys problem
lies somewhere in the inbetween. After 7
days and nights of little to no sleep due to
the emergency surgeries needing to be
performed, i think my baby has a few loose
wires. Fingers crossed comrades, im going
in. Chris Sypher has spokennnnnn!!!