2004 Nissan Titan down shift

What do you mean it accelerates when it down shifts? Are the RPM's staying high?

when I'm holding the brakes to stop. as soon as the rpm's drop to a point that it needs to down shift, it accelerates. even though I am holding the brakes it acks like the truck pushes the gas pedal by it self. if u dont keep a good distant the truck will make u crash.

That sounds dangerous. Have you checked the idle air control valve?

no I did not replace the idle air control valve.I called the dealer yesterday to find out if the truck has one cuz non of the part stores said they carry that for a titan. the dealer said it sounds like a torque converter but bring it in to do a diagnostic test. what do u think about the torque converter. when I replaced the trany I kept the old torque. and don't remember it doing that. but my brother says he does. he's the one that drove it home I just took it for a quick test drive.

I'm not sure how the torque converter would increase the engine's RPMs. I have, however, seen torque converters that don't allow the engine and transmission to release and when coming to a stop, the engine would try to keep going.