Aluminium bullbar and fuel tank streaks

I have noticed the last couple of times I've 2 stepped HF on bull bars and fuel tanks they are streaking, admittedly they have been neglected for a number of years. Is there a way of counter acting this? They are white Alum not polished. Although, I never have any issues with the stainless components they turn out great.
I run the HF at 2% thru shur-flow then hit with 4% caustic hot downstreamed soap after two minutes dwell time and I apply HF bottom to top.
Could I be running the HF to strong or two weak? It doesn't apear to be removing all the oxidation probably 80% + I am not letting the acid dry before applying soap.

I did have some reasonably good reults a couple of months ago with 20% phosphoric instead of HF @ 2 %.

Wow that was quick.....................
Larry they are white, so I am getting an uneven two tone finish with no brown present, as I said these trucks live in toxic waste dumps so they are not the best kept.

Thanks,
I'll make up a special 5% mix to burn down to the white aluminium lustre the fuel tank will be fine, but I'll make up a jig to cover the windshields for the bull bars.

I'm fighting a little devil in my head that wants to try downstreaming the 40% HF and upstreaming the soap, but I can't seem to get my safety sam side around it. I guess it's like climbing a tall tower the more often you do it the more comfortable you are with it. One step at a time!!!!!!!!!!!!!!!!!!!!!!!!

I cleaned a Fast Vac last night it took me 5 hours of first rotajetting the super phoshate off it just to get to the paint work to allow the chem to work. It spends most of it's time in a fertilizer plant cleaning up spills from the conveyors, boy does that stuff do some damage the sulphuric acid corrodes everything electrical, paint chassis you name it. Rewire every 6 months, new paint annualy, chassis inspection 3 monthly.