Transmission won`t shift to 3rd
 

On the 2001 Blazer ZR2 1st and 2nd shift fine but when it hits 35mph it doesn`t seem to want to shift to 3rd, What is causing this-is it something I could fix or will it need a rebuilt transmission?

Does it still shift into third eventually? Have u tried manually shifting it? If it still shifts into third but late and hard you could have a sticking shift valve

Mine is '01 with similar issue.
 

Noticed that Blazer wasn't shifting from 2nd to 3rd. Hooked up computer and showed Torque Converter Control Solenoid was bad, so did a swap of the TCC, and BOTH shift control solenoids.

Still not shifting from 2nd to 3rd. Did check the valve in the one control solenoid slot, moved in and out nicely, so no issue there.

NEXT??