Bought a 99 silverado back in December on Christmas eve. It had a 4l80e. But had issues. So i bought a fully built 4l60e trans w/ a 3k stall. Whoever installed back at this trans shop they told me they repinned the harness i guess a plug that connects to trans. So i got it towed to my house & got a street tune. But did realize my truck wont go into park if i put it in park it acts like its neutral. So i use the e brake when parking. When starting it, it wont turn on in park, it turns on in neutral. I need to bring my lever down to 1st gear 2nd , 3rd , D & N. Then it will turn on. I cant put it on P then R & finally N. It wont turn on i need to work from my 1st up to N. But when driving my trans wont hit 4th gear which hits around 40mph due to my tune. Again 1st 2nd & 3rd run great but 4th wont hit. UNLESS when i gun it, you can see the rpm rise & see it drop back down & feel the truck hit 4th. Thats only when gunning it. It wont shift when cruising.

 

what a bunch of gibberish

if you paid a shop, take it back and have it made right

 

I did & they keep having me pay for extra stuff. Which im not gonna do. I did buy a adapter for the harness, neutral safety switch & cable for the lever but they said they already did all that. But they say it will take 2 months. Im not going to wait 2 months. I was told that it takes 2-3 days to rebuild & install the transmission no longer than a month.

 

I would start by checking the shift linkage adjustment.

 

Not holding Park... sounds like the Transmission may have to come completely apart.
I would do what the others have said, and bring your vehicle back to the business that did the Transmission.

Times like this, cause me to remember evil children with 100 HP cars, that would "Neutral-Drop" their Transmission to chirp the tires...
The next thing ya know; the Transmission will not hold park...
Because they shattered the Output Ring-Gear and the Parking Pawl has nothing to latch on to!
LMAO!!!