2002 Chev Transmission - what do I have?

[Don in E Texas]

Recent owner of a 4 window Chev school bus with the Duramax 6.5 engine. My question is about the transmission. Is it an Allison or??? I've had three oil change guys look at the transmission and all have said there is NO spin on filter. Wonder what I might have? Any thoughts?

Thanks
don

[cadillackid]

most of ther Van chassis GM busses got 4L80E transmissions

[BamaBus]

My 02 MicroBirds didn't have the RPO codes located in the bus, but I was able to call the local Chevy parts dept and they gave me info of the trans, rear end ratio etc. using the VIN.

[PorchDog]

I asked a service techniican, and he said it was probably a 4L80. The six speed 6L90 came out in 2006 or 2007. We are pretty sure all Allison's have a spin on filter. My thinking is that the Alllison would physically not fit in the van chassis.