I live in MN so am biking in wet/snowy/salty conditions on my 5mi commute to work & am relatively new to bike maintenance.
2 weekends ago I washed my chain & drive train with the park tool chain cleaning device and a stiff bristled brush for the cogs & sprockets. I then re-lubed the chain.
Afterwards, I've been having trouble with the rear derailleur getting stuck when shifting down to the higher sprockets. I can shift down just fine, but can't shift back up. Sometimes I'll get stuck at the largest sprocket, but other times it'll shift to the 2nd or 3rd largest sprocket before getting stuck. The derailleur in question is an older shimano deore.
Last weekend I took apart the derailleur completely and wiped it clean as the pulleys were full of gunk. I then re-installed it (didn't reapply any sort of lube as I wasn't sure if it used/needed any) & tightened/adjusted the cable so it indexed properly. Everything appeared to work fine on my commute to work the next day and it shifted up/down appropriately. However, on the commute back home it began doing the same thing again where it'd get stuck on the larger sprockets and wouldn't spring back out. If I shift it by hand it still works, but I can't get it to shift using the shifter.
Any ideas of how to get this fixed?