P0700 will come up with most all codes or faults to do with a transmission,P1781 is 4X4 switch out of range,I have never heard of a P1721 but a P0721 is trans output sensor range or performance.If the computer isn't getting a output speed it doesn't know that it should shift.I would check all your wiring down around the trans area looking for broken or grounded wires if ok have the speed sensor checked for being opened.
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