I have just replaced my chain on my Marin hawk hill and the chain is slipping, I've placed the chain alongside the old one and made it the same size and upto now I've removed about 8 links using the propper tool, the chain feels ok when I'm in low gear " biggest cog on the rear" but when I'm putting strain on the peddle and using the smallest cog's "7th, 8th and 9th gears" it's slipping like mad, do I need to take more links off?

probly you put it on wrong or you broght the wrong size

It`s not tight enough , adjust your deraliar, or take a link out...

Sounds like it to me.

Ur going to have to size the chain so that it is taught on the highest gears and still large enuf for the lowest gear of largest cog. I know, it can be frustrating, but it is a matter of tweaking.

i think you need some links taking out of the chain needs to be tight,xx

I have the same problem right now only on a road bike. Check the chainrings in the front or cogs as some people know them. They could be worn out. If the teeth on the cogs are worn, it can cause slippage. Check the cassette too. You might have to replace both. Usually when I buy a new chain I replace the cassette too.

If its actually slipping and you've made sure its got the correct number of links, then chances are the teeth are worn on the gears that are affected.Its also possible that the derailleur is actually phantom shifting, which can feel like slipping, and occurs mainly when you apply a lot of pressure to the chainset, such as when you're in higher gears or riding up a steep hill.If its this, then you need to adjust the derailleur/s so that they have the correct alignment, then your chain will stay where you expect it to be.