Problem with TC for G5

[shocky]

I jus bought a vitacon 2X TC for me canon G5.
1.Paid $85 for it, wonder was i overcharged (Sry dunno prices for equipments)
2.After fixing it on, I tried full zoom, at my G5's 4X, which means i should get 8X with the TC right? however comparing to without the tc, but with digital zoom, the 1st pic actually less zoom than the 2nd, which is only using 6.5X, not 8.1X. Is this normal? or was i given a 1.4X tc instead?
3.When i zoom max and shoot with the tc, seems like off centre shots are blur,the overall pic also blurer by abit is this normal?

i would like to know the above probs r common for a tc or is it jus this tc i bought..

Btw another qns i have is that even when i shoot at max quality 5MP, the image when blown up to 100% in PS, its blur and abit pixelized and poor quality, basically not good to crop and view at 100%, must sharpen and resize. On the other hand, images fr a D70 look still ok at 100%. Is this to be expected from a non dslr proconsumer cam?

thanks in advance