What would cause a 94 Toyota 4 Runner V6 automatic transmission to take 30 seconds to go into reverse?
All the time or just after it has been sitting for a long time?
Is the fluid level normal? Low fluid can do this.
Just after sitting for all night or after work. Once it gets going it seems to work normally. I just had a trans flush and service from my trusted mechanic.
Did the problem start after the flush or was it happening before? If just started verify the transmission fluid level.
It started before the transmission service. My mechanic and I decided the service “couldn’t hurt” and might help. With 163,000 miles on the trans I’m lokking for a repair instead of an overhaul.
This depends. I’m wondering if it enters reverse quicker if you mess with the shifter a bit? Also, if you go into drive without first reversing, does it bite right away?
It’s hard to say because this transmission may be fully hydraulic or may have electronic controls. Transmissions that pick gears hydraulically use a main valve which is hooked to the shifter in the car via linkage. When you engage a certain gear, the main valve directs fluid pressure to whatever circuit(s) are necessary to establish drive in that selection. So if you shift to reverse, fluid pressure is directed to the circuit that engages reverse gear. When you drop into drive, the fluid pressure is routed to the decision valve circuits (named decision valves, obviously, because they determine when to execute shifts.)
But I beleive a modern electronic transmission would use a solenoid to direct fluid pressure to reverse, drive, etc. I’m not sure if it uses a main valve.
Either way, the linkage between the shifter lever and the transmission is the first thing to check. If the fluid level is good, and drive checks out, then as stinky as it seems your reverse may just be on the way out. At 163,000 miles, any transmission would be starting to get tired. The seals in the reverse clutches may be feeling their age, causing a delay in buildup of enough pressure to apply the clutches and lock into reverse. Does she shudder or groan when reverse finally engages? If you hit the gas, does it clunk in?
Try raising the engine speed above idle, maybe around 2K RPM as you wait for reverse to engage. Be ready to hit the brake as the car may jump. See if reverse comes up any quicker; revving the engine turns the pump faster, giving you more fluid pressure available to apply the clutches.
It may be rebuild time… sorry friend. 
-Matt