Chain slipping on a self-repaired bike

[toor]

I'm stuck with a problem of chain slipping on my old bike that i wanted to fix myself.

I changed the whole drivetrain and maybe this is as simple as a mismatch since i have about zero experience in bike maintenance, i tought you would know for sure.

Here are the components i chose to put on based on 8 speed compatibility and cheapness:
Front Derailleur: Shimano Acera FD-M360-6
Rear Derailleur: Shimano Acera RD-M360-SGS
Front Chainset: Shimano Acera M361 triple set square taper (42-32-22)
Cassette: Shimano Acera HG41 (11-30)
Chain: Sram 8 speed PC850
Stock 8 speed shifters (replaced wires)

To be more precise every rear gear tend to make more or less my chain slip forward when i press the pedals (even moderatly), being a bit more slippery at the smallest cog then at the middle cog.
Slipping happens as regular as clockwork, always after the same amount of pedaling.
I have no problems with staying in speed or with shifting (altought my tuning could be better) and only find answers for that when i try to google my way out of this slippery chain problem.

Could it be:
-inaccurate rear derailleur alignment?
-chain has one excessive link?
-mismatch in components?
-rough rear indexing?

Thanks for any advice.

[cradom]

Go here and make sure your derailleur is adjusted properly. http://www.parktool.com/blog/repair-help/rear-derailler-adjustments-derailleur
Also make sure your derailleur hanger is straight.

[cny-man]

Need a better description - under what conditions does it slip - front/rear combo(s), pedal pressure, shifting to larger or smaller cogs?

[toor]

Alright, this topic could be closed because will eventualy bring that bike to a pro since i almost finished to waste it.

Thank you for your answers cradom and cny-man.

I checked the (rear) indexing which was already good, every gear went up and down smoothly and stayed in place.
I could not check the rear derailleur alignement since dont own the proper tool, so got the bike out for a test run.
Since i had no trouble shifting on the rear cogs i planned a skipping test on every gear to bring more details about my problem.
At that point i went to the speed 1-1 and started pedaling while hitting the brakes to stress the drivetrain and see how it would skip, but it didnt, the chain broke open and i quickly noticed the rear derailleur was against the rear cogs as the hanger was badly bent inward.

I'm not sure i want to replace to hanger and finish the tunnings myself since this repairing experience is getting worse and worse.

[cny-man]

If you post more details please don't describe gears as "1-1." We need either tooth counts (48-13) or relative position/size (smallest rear cog, 3rd rear cog in, large chainwheel (front) etc.