Ill be in drive try to hit 1st gear at 40mph but cant ill only hit 1st gear at 35mph i do have 373 gears with the 5.3
will a hhp3 help me out?

 

Nope .. that's a 'feature'.

They do that so you can't over-rev the engine. It will also keep you from dragging the tires when you make that downshift. I think a shift kit will help you out. If you do that, you may want to look at new servos too.

 

I am almost positive the diablo predator can fix your shifting issue. You can use the predator, which I just got for my 03, to tell the GM ECU when you want the tranny to shift. This can all be done by adjusting the mph and rpm shift points.

I HIGHLY recommend getting a diablo. So far I luv it. It really has the truck driving like it should! It basically also deletes torque management so now I stab the gas off the line, the tires bark a little, the posi locks and the truck hauls! I also have the rev limiter set at 5890 rpms so when at WOT every gear pulls this high. Its very nice!

 

I can but i also have a Z71 with taller tires than you so my effective gear ratio is higher than yours.

One thing I found interesting is some people say their trucks wont let them manually shift them and that the PCM will overide you and shift itself yet mine and a few of my buddies trucks dont do that. If I left it in first gear and floor it it WILL hit the limiter, some say theirs wont. Maybe this is something similar?