VR V6 won't rev

[luxadore]

Hi, I have just finished installing a VR V6 and auto transmission into my hilux but am yet to fit an exhaust up to it yet, I have the engine pipes with the O2 sensor and the catalytic converter fitted but the whole set up feels like crap to drive, I test drove it around the block a few times and it feels like it doesn't want to rev, when I put my foot down it coughs and splutters like crap and when I lift my foot off I get a small blip in power and thats about it, I am using a pod air filter for now until I have a 3 inch pipe bent up to join up with the hilux air cleaner assembly
I don't have any error fault codes on the PCM so I think everything is wired up well and working ok
Would the lack of exhaust back pressure be making the vehicle behave this way?

[camstatic]

Sounds like throttle position sensor isn't reading right... I would also theck the MAP sensor

[VR38]

Plug lead loose, vacuum leak?

[luxadore]

Bit of an update.
I had an exhaust fitted today, just a 2 1/4" single muffler system and went for a drive it still feels crappy and hesitant to rev up under load. (past say 20% throttle)
my fault light isn't illuminated so am guessing all is well sensor wise but one thing I should tell is that when I did the coversion I had to drain my diesel fuel tank and run about 3-5 liters of unleaded through and let that drain out completely before filling the tank with ultimate 98, could there be some residue diesel or moisture in the tank mixing with the fresh fuel causing the problem?
I can get the car to cruise along at 80 in D with the torque converter locked up but anything faster than that sees the transmission drop back and stay in 3rd with no lock up and it feels like the engines working hard

[luxadore]

I have a feeling it may be a dodgy coil pack, causing spark to break down at higher loads, I have borrowed a set to swap over and see if makes a difference