4.5 liter with flat spots

hi all can someone shed some light on what may be happening with our trol or point me in the right direction...
when i try to accelerate from basically idle up to about 2500rpm it doesn't want to get in to it as such, it has a bit of a hesitate and has pretty average sort of performance for a 4.5 liter from low end to mid range.
the truck has done approx 153000ks i have only owned it all of 3 weeks.
i spoke to the local garage (non nissan) and they mumbled spark plugs which i replaced with super dooper top of the range bla bla bla platnim plugs... 110 notes!!!
made no difference just made me broke and fustrated lololol...
i have changed the oil and filters (oil/air) while i was at it, will change the fuel filter tomorrow now that i think of it (ooopps).
any help would be greatly apperciated before i take it to nissan to replace/clean a $50 part at a cost of $400 notes (you know what i mean lolol)...
it has a manual transmisson too...

Good idea changing the fuel filter tomorrow.
Other things to check, distributor cap for water, cracks and make sure the carbon pin in the centre is still intact and spring loaded. While the dizzy cap is off check the condition of the rotar button. If you have a timing light check the ignition timing. I can't help with timing spec, I've never owned or tuned a TB45. I would expect it to be around 5 to 10 degree's BTDC.
Another thing you can check for is a blocked exhaust. Drop the exhaust before the cat. converter and see if that get's rid of the flat spot. Just don't do it before 9am on a Sunday, unless your neighbors are having a big party tonight!
If all that fails it's time to do a code test (you can do that first if you want, but I prefer to check the basics first), and see if that gives you any clues. Do a search on here for "checking and erasing fault codes".
There are a few good 4WD specialists around the mudflats, so you shouldn't have to go to Nissan to find the answer.

Tony

cool will do as you said tomorrow many thanks will keep you informed...

Hi mate
Ive got a 4500 too had similar problem found it to be the oxygen sensor in the exhaust once changed made a big difference. Also check the plug leads big cube engines need good spark. My 4500 is no v8 super car either, Ive driven a couple and all felt a little sluggish until about 2000rpm. Ignition timing is 5 degrees plus minus 2 degrees with the throttle position sensor disconnected.

happy trouble shooting

Scott