Hi Torpedo Chief
I think it's a LVTH 5 - Landing Vehicle Tracked Howitzer - mounting a 105mm Howitzer to support beach landings. Built for the US Marines, I think they're still used by the Philipines. Somewhere along the line the designation was changed, not sure why, but that is why this is as it is whttp://www.primeportal.net/apc/stephen_sy/lvtp6/ 
The original LVTP6 was a proposed vehicle - prototypes were built, but not put in production - based on the M41 chassis - actually on one of the APC's derived from the M41.
It's designation was also changed to LVTPXX, there was also a version mounting the AA turret from the M42 Duster, plus a Howitzer version mounting a 105mm, but in a new design turret

Mal