Serpentine belt fell of

[Oskari]

3l v6 (asn) and serpentine belt. The belt comes off if accelerate hard. The problem started when the ac compressor got stuck and broke the old belt. The current one is 6x1880, but I read that the oem is 6x1878. Could this be the fault? Now I have changed the belt tensioner, alternator and ac compressor. The belt rotates directly and does not resonate.

[Steve Q]

It could potentially be the fault. 

Ac compressor not seized etc? 

Also I believe lower pulleys are known to come loose on c5s. I had this on my 2.5 diesel