Getting and maintaing low temps? If so, two choices.
1. Needle valve. Lots of threads on this. Do a search on this forum, a ton on info on that.
2. Cut back on the flames by blocking a few gas outlet ports on your burners. Use aluminium tape used by the HVAC guys (not aluminium looking tape) as a test on a few ports and check the difference. If it lowers the temp, use hi-temp (1000 F) silicone to plug the ports.
If your smoker is very well insulated then the "off" (no heat) state in the burn-no burn cycle still generates more heat than needed. Blocking ports cuts down on the heat generated on the burn cycle. Keeping the exhaust vent damper fully open will also help. Cutting air intake will choke the burn.
Might take a combination of the two. At least the silicon plugs can be cleaned out and the needle valve opened fully to get back to where you started.