I’ve been having this problem for a while now I changed out the trans to one for a junkyard that ended up being garbage so I rebuilt my old one and put it back in hoping a rebuild would solve my problem, I can get it from first to second but won’t go into third just high revs I did a rebuild kit with new steels and clutch packs I bought a whole remanufactered valve body with new all new sensors and seliniods and a remanufacterd torque converter the only thing I didn’t replace was my vss which I thought could be my problem but I put it on a ohm meter and read out .69 which on the video I watched is what a new one read out so I don’t know anything else that could be cuasing this hoping someone else does

 

You might find this troubleshooting chart helpful...

 

Might want to do a pressure test also. It's on the last page.
https://trucktransdiag.com/downloads...nsmissions.pdf