Large Caterpillar ID

I found this crawling along the ground, in an area of tall grass and bushes, in the very North East corner of DRC. (Small town called Adi, west of Ariwara) Sorry, I can't get very good pictures of it... it moves pretty quickly and I'm avoiding handling it directly. Anyways, I've had it for a few days now and have been trying to figure out if it'll pupate, or if it has more growing to do. I have zero experience working with larvae like this, but figured that at it's size it must be nearing that stage. It seems to like dirt and occasionally will bury itself in it (it digs by grabbing small rocks or chunks of dirt with it's large mandibles).
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Thanks for any help you can provide!
Tom