Mankypurple

Vehicle: 197 C20. Engine is a new rebuild. Original block 350, high compression build, mild RV can, Holley 4 barrel, polished heads, flow master exhaust. Trans is a Turbo 400. I didn't do the work on the trans and I am meant states away from the guy to use him as advice. Transmission was rebuilt, they put in heavy duty valve bodies for towing, a medium stall converter, and stage 2 shift kit. Has a solid rear axle as well

I don't know if it's a problem as I am getting conflicting answers. What I'm having happen is at wide open throttle, the truck will not shift to 2nd. Itll stay in 1st until the engine blows or I let off the gas. Seems wrong to me, but I've been told it's because it was built to tow and handle torque and weight, that the valves hold it there so it doesn't slam with a potential load being towed. Also was told it was a kickdown cable. Unsure. Next issue, if I'm cruising at 70ish and decide to pass someone and give it the goose, itll skip down shift to 2nd and go into 1st, which, takes me beyond redline. Occasionally, itll hit 2nd on downshift for a short moment, but no matter how I feather it, itll go to 1st a second after shifting down from 3rd.

so I need a trans guy to give me some pointers on how to correct this, be it adjust a cable or swap out valves. I can do valves, cable I am sure I can figure out.

Thank you