Land Rover Repair: 1998 LandRover Discovery I, specialist shop, sensor readings

Question
I have a 1998 Disco I that runs at an idle very smoothly and sounds great, until I try to reve the engine or get any power out of it. Anything above 1000 - 1500 RPM's and it backfires through the exhaust and intake, and won't go anywhere. The OBDII gave a readout of  P1316 - P1313 - P1314 - PO300 - and PO301 through PO308.
Please Help! I have, at the suggestion of Motorcars LTD., replaced the heads to no avail.
Thanks for any help you can offer.
Robin

Answer
Problems like yours are generally solved by looking at the live data screens on the scan tool at the time the engine is acting up.  You should be able to see one or more "off" sensor readings that will point you in the right direction.

If you don't have access to a scan tool with that capability you'll be well advised to seek a specialist shop.