Is it true the confederate constitution stated that each state was independent but must guarantee the gradual end of slavery in confederate territory?

No, that statement is not accurate. The Confederate Constitution, adopted in 1861, emphasized the independence of each state and explicitly protected the institution of slavery. It did not mandate the gradual end of slavery; rather, it allowed for the continuation and expansion of slavery in Confederate territory, reflecting the Confederacy's commitment to maintaining and preserving the practice.