Bucking on Hard Acceleration

Check your EGR system.

Are you pulling a trailer or have a heavy load - you should not drive in overdrive in those conditions. You will eventually ruin your transmission.

Could be a transmission problem or something as simple as bad spark plugs.
The engine is under the most load when RPM is low and you are trying to accelerate, such as when it upshifts.
You should have the computer checked for trouble codes and hopefully that will point you in the right direction to test.
If the spark plugs have more than 50,000 miles of wear you might start with replacing them.

use a couple of cans of injector cleaner as faulty injectors are indicated

It could be a single ploblem or a combination of the fuel system the engine could be starving for fuel or air or the timing is not set correctly. The transmission may need some adjustment.

well, there are a few things you can try! a bad tps ( throttle position sensor ) transmission shift issues, bucking, jerking, idle surging,engine cutoff, hesitation on take off, surge while cruising down highway. also be sure your fuel filter is ok! and not plugging up. a maf sensor symtom is surge, slip condition under load, the mass air flow or MAF may be degraded or contaminated. stalling, misfiring, poor acceleration. a light may not come on. you can go to any auto parts store and buy a spray can of maf sensor cleaner. follow directions on can, and this should help alot. good-day!!

sounds like your egr valve is opening too far at part throttle and sticking open. it is actuated by solenoids that open and let engine vacuum in. you were on a good path in checking the vacuum lines. however this may require replacing the egr valve and gasket. the egr valve is circular in shape on top and usually is bolted down with two bolts. its located on the engine side facing the firewall.

That sounds like a bad tourqe converter.

I have a 2003 Nav with the exact same problem. I've found it diminishes when taken out of overdrive. Also it's intermittent but more towards bucking. Sorry to post this under solutions.

The evaporation canister can cause this, so would any vacuum leak. A faulty throttle position sensor or camshaft position sensor would also cause this but it would in the diagnostics most likely.