Hello! I am new to the forum! I own a 2000 Chevrolet K2500 (not Silverado) ext cab 4x4 with a 454 with 60k miles on it that I picked up damaged and I have since re-built it. I also own a 1999 GMC K2500 4x4 Suburban with a 454. I must say that I enjoy the 454 and 4 speed combination. I dont do any heavy towning at all with these 2 trucks, these are daily drivers. I am posting on this forum is to ask the question why GM does not offer the 4 speed transmission with the new 8.1L big block in the 2500 HD pickups? I have tested out a new 2500 4x4 Suburban with a 8.1L and the 4L80E/4-L85E transmission combination. It had more power and torque then my 99 Suburban and 00 pickup. I then test out a 2500HD pickup with a 8.1L and Allison transmission, Extended cab (same configuration as my 2000 pickup). After driving the 04 pickup with the Allison, the 04 Suburban with the 4L80E/4-L85E transmission combination and my 99 Suburban and 00 Pickup have more lower end torque then the 8.1L and Allison transmission. I was very disappointed with the 04 2500HD pickup. I did not like the fact around 45-50 mph that the Allison shifted between 4th and 5th. It was up and down the entire test drive. It would be nice to see GM offer the same combination of the 8.1L and the 4L80E/4-L85E transmission combination that is in the new 2500 Suburbans with 8.1L as a option in the new 2500HD and 3500 pickups as a option instead of having just one transmission option. Some of us like the big block as a daily driver.