BMW 5 Series engine keeps cutting out

I have just posted a problem re my 5 series with a starting problem. I've been told by many people that the fuel pump relays are bad for failing. You get a carbon build up on the contacts which breaks the circuit. They are only about £6 and easy to replace. It may be that you are getting a bad contact while driving. It's worth a try!!

It was working fine but now when i start to drive it does not speed up but when it gets momentum then it runs like any normal BMW. But the start is very slow and even when i press down the accelerator, it does not catch speed. in fact when it goes up hill, it gets slow. when stopped, i want to check if the problem is with accelerator, i press down the accelerator and engine sounds fine, strong but if i press accelerator too much it starts giving odd smell of burning. It also keeps cutting out and i have to keep my foot on the accelerator. My friend says it`s clutch. but i doubt if its clutch then i should have problems ahile changing geras that i don`t have. gears change very smoothly. Can you please guide me?
thanks.