Bicycle Mechanics - New Shadow rear derailuer or rebuild?

I have an '05 Trek Fuel EX-8 with a long cage Deore XT rear derailuer and have used it regularly the last 2 1/2 years. The problem is after a few LBS tune ups and derailuer alignments the rear gears still want to "walk" or shift when they want. I have replaced the chain and the rear casette already and was thinking maybe the new "Shadow" XT Deore would solve the issue. http://bike.shimano.com/publish/content/global_cycle/en/us/index/products/mountain/deore_xt/product.-code-RD-M772-SGS.-type-.html
Is it worth replacing or rebuilding the springs etc. at this point or for around $80 getting a new one? I was looking at the Park site and they go into rebuilding them but I am just so sick of the constant mis-shifting that I could scream :wtf:

Thanks for any help here!

you need to adjust the tension on your shifter. you don't say what kind you have?when it is lose you will have this problem.

you need to adjust the tension on your shifter. you don't say what kind you have?when it is lose you will have this problem.

I have been all over the map with different tension and I think the derailuer might be a little loose itself, I looked in line from the back and when it flexes under tension I think it looses it's alignment because it will grind in and out much of the time. I think this derailuer might need replacing if that is the case.....right? How can you tell if the derailuer is good enough to keep using and not waste cash?

the pins in the dérailleur have gone bad after years of service. it hard to tell sometime, the best thing to is take the dérailleur to your lbs and compare your old one to a new one. due to it age yes it time to replace it.

I just bought a new one off Ebay for $75 and I figure I will need it soon if not right away. I am going to attempt to install it myself using the Park site and a repair book I have. Thanks BF