Shimano 105 gear change won't stay tuned A bike shop replaced my cassette, and chain on my 105. After about 70 km the shifting starts to deteriorate - slips,skips or noisy operation. This type of rapid deterioration occurs after every tune up. Best I can expect from the 105?
Any named series shimano, sram, or campagnolo setup should work for thousands of miles/KM without much attention.  

Where you are riding may be an especially dirty area or there could be moisture (puddles count as moisture!) that could be causing you an issue.  Also, your bike storage location could be causing water to enter your housings and causing problems.  And finally, if you routinely put your bike down on the drive side... that causes all sorts of difficulties.  

Really need to know more about your issue, but poor shifting performance can be caused by:


Cable/cable-housings that need to be cleaned, re-lubed, or replaced.
dirty chain
chain that needs to be lubed
chain that needs to be replaced
worn out cassette
bent Rear Derailleur hangar(e.g. damaged)
bent Rear Derailleur (e.g. damaged)
worn out Jockey Pulley
Rear wheel installed crooked (hard to do on most bikes, but non-vertical rear dropouts are susceptible to this, especially when a quick release is involved.)
sometimes a 10spd chain used on an 8 speed cassette/chain-ring can cause issues (but not always) or a 9spd used on an 11spd, etc.


Firstly, I would check to see if your rear derailleur is in-plane with the cassette. If the RD is bent, the hangar is bent, or the jockey pulleys are worn it'll be very finicky to keep in adjustment.  (e.g. nearly impossible...)