How can I fix my corsa I'm too poor to buy a new car! Help?

For the past 6 months my car will shudder when you first turn it on and then after 5 odd mins will sound as though running normally, but when driving it will lose power if you try to accelorate over 40 or go up hill even slight inclines also when going round corners and sporadically when at lights or from sitting in traffic it passed it's mot with flying colours and has been in the garage 10 times I had a service and the diagnostics showed mass air flow and lamba sensors both were changed no difference the egr was changed
no difference does anyone know anything no garages or vauxhall themselves have an answer please help before I go insane!!