How much fluid did you start with? C6 holds a lot
I mentioned this earlier, worded differently. Dead-empty as much as 12 quarts. I've installed many-a C6 over the years and depending the amount of drain (and even a USED replacement I would drain off converter also whenever possible) On a trans I knew was completely empty, I would add 6 before start-up, add 4 more once running and then begin to check. Keep in mind, some fluid clings to the walls of the dipstick tube for several minutes after adding which can scrape some onto the stick, this can give a false-read. Once I am sure it needs more, I begin adding 1/2 quart (1 pint) at a time till I get near, but below the full HOT mark. W/rear wheels raised, take it for a spin, beginning in Low-1, shifting up to 2nd and then into drive. From Drive, back down to 2nd, then Low. I then will brake wheels to stop, go into Reverse once, then back through the gears one more time and recheck. Add fluid as needed, no more than 1/2 quart at a time to prevent overfilling. ALSO, if overfilled, not panicking because this is a rather easy fix too.