97 Chevy k3500 4l80E hard shifting, No OD, New to me

Hello all, I am a proud new owner of my first diesel truck, I come to yall from the Lexus realm actually, as I have a 2011 Lexus ISF. Now to my concern: Just picked up a 1997 Chevy k3500 Cheyanne, 4D with the 6.5 Turbo. Independent of any specific ambient conditions, the vehicle shifts hard into gears 1-4 and slightly hard into R. Same feeling when pressing the accelerator pedal while in motion at a low-moderate speed. There is no overdrive either, the speedo is inaccurate by at most 10mph at higher speeds. It does feel like the TC locks in 4th, after I let off the throttle, I almost have to persuade it to lock. The truck wants to top out at about 56mph and after that it just redlines. The fluid is red on the stick and slightly high when I checked it cold. I have an ABS MIL but 0 codes have been set for any module or system, no CEL. I have checked the ECTS and that checked out. I am a tech, but transmissions are above me, unfortunately. Any help is appreciated. Thanks everyone!