Transmissing noise (click click)

Ok, so I can get a new discussion on my crappy jeep. It's a 1995 Wrangler 6-cyl 5 speed. It's lifted 3 1/2 inches and has 33x12.50 tires. I have re-built the engine and replaced the clutch 2 1/2 years ago. About 4 months ago I noticed a faint clicking noise coming from the transmission every time I would let off the gas when driving in 2nd and 3rd gear. Well in the last week or so the noise has gotten louder in all gears. I'm pretty lazy so I haven't checked the fluid levels in the tranny or t-case, and I don't have a socket big enough. This weekend I was thinking of changing the fluid in the tranny with 90w-140 instead of 80w-90 gear oil. Is that a good idea? I know I'm going to have to replace the transmission. Anyone have an idea on how much I should pay for a used ax-15 tranny. Do you think a junk yard will let me go remove the transmission from a wreck for less? Last, when removing the tranny, can I just unbolt the tranny from the bell, or do I have the unbolt the bell from the engine?