Good Afternoon,

I have a 1999 silverado 1500 4.8 single cab.

I started having the following issue after the transmission was rebuilt.

as im driving and I step on the gas the engine stalls for about 3 to 4 seconds. when it stalls I tried pressing the gas and there is no response from the truck until it kicks in on its own.

I took the truck back to the transmission shop and they are telling me its not the transmission.

i ran the codes and the only code showing up is the p0420 because when i bought the truck it had no catalytic converters. I recently replaced the upstream o2 sensors bank 1 and bank 2.

I uploaded 2 videos on YouTube

https://youtu.be/mzCMxHD0DdY
https://youtu.be/oKTodbyubFY

thank you in advance for your help