You don't adjust the turnsiginal speed. It is determined by the resistance load on the metalic strip inside the flasher can, and if everything is right, it will click and blink at a normal, consistant speed.
This might be a stupid question, but what is acting up, the dash indicators, the lights themselves, or is the clicking noise varying?
It coulo be the Insturment panel voltage regulator (not entirely likely), battery voltage regulator, or flasher can. The IVR is $40 or so, an elctronic battery regulator is $10 from Autozone, and a flasher can (clickey thing) is $4. It could be that you have some funky wiring, corroded bulb sockets or intermittently working bulbs, which could vary the resistance load on the flasher can and make it click at different speed.
Also, why did you replace the battery, had it been boiled over? That would be a sign that the battery voltage regulator is bad and overcharged the battery siginificantly for an extended period of time, causing it to boil the fluid out and ruin the battery. To get a more precise diagnosis, more details are needed.
The squirrels in my head have spoken.
Cobra 5.0L & AOD swap, here we come.