I agree. The transmission shop where I had my Impala SS tranny built, uses nothing but Amsoil.

 

Agree with the synthetic rcommendation. Using Amsoil in the 5.4L and should do the same for the tranny. Peace of mind means a lot . . .

 

I don't think the 4.6L is a very powerful engine. My sister has this engine in her Expy, and it seems barely capable of pulling the vehicle along. I have a 99 Expy with 5.4L and tow a 26' travel trailer fully loaded and have no problems with power even in hilly terrain. It also has a 3:73 rear end with 16" wheels. I don't know what size your wheels are, but putting a 3:55 rear end in there doesn't sound like a very good thing unless you are trying to improve highway mileage. If you are locked into this truck, you may want to look at having that rear end upgraded if you plan to do much towing.

 

I'm sure it's not the wind drag. Cruising at 60-52 is no problem at all in the Midwest. It's the getting out of the hole that is the problem, and I'm at 6,000+ pounds. That makes me think the real issue is the tires. If I recall, these Michelins weigh quite a bit more than 15 pounds over the stock Pirelli's. Mine are load range E. I'm just about sure the rolling resistance is killing me. My 2007 F-150 (close to identical truck - not KR, though) was alot faster off the line... a minimum of 2.5 seconds faster to 60mph with 18's and steel wheels. These aluminum 20's and E's are tough.

 

Sorry for the delayed response...

I'd only go the expense of additional 17" rims/tires setup IF I towed alot. I've run my truck about eight weeks (driving) and am close to 13-14k. That's mostly empty. I've drug our TT about eight times this season (four more to go, or so), and I'd still not spend the money for smaller wheels - even though I see it probably affects my daily mpg, too. If you drag several times a month, then I could see it. Next time, I'll reconsider 18" wheels again. I'm still thinking the E-rated Michelins I have are substantially more heavy than an 18" BFG or 20" Pirelli P-Metric.

 

I got to say, i am surprised that some of you with the 5.4 are disappointed with the towing capabilities of the truck. What makes it harder to believe is that live where it is generally flat.

here is my '05 with our old trailer which when loaded weighed in around 5k lbs.





I would routinely climb the mountain ranges here in Oregon at 60-65mph. I roll down the freeway at 70-75mph like it isnt there. I generally pass just about all Ford, Chev and Dodge 250/2500 and 350/3500 that were also making a towing climb. Only the steepest passes really work the truck hard.

My truck is 100% stock. Granted, i fully expect the truck drag *** more towing a load near the limit, but some mods should remedy that.

The new trailer were are close to buying is heavier by a couple thousand i dont expect a major performance hit though.

 

I'm reading this thread with interest as I am in a similar boat to some others. Earlier this year, we traded my '99 F-150 Supercab, 4.6, 3.55ls, 2wd for a more family friendly Expedition (2001, 4.6, 3.31ls, 2wd, sport package). While I knew the expy was a bit heavier by about 400-500lbs and had taller gears, I was hoping the improved 4.6 would help. The 17's ate technically are slightly less diameter than the 16's on my 150 Lariat, 30.6" on the Lariat and 30' on the Expy. I can still pull my 4200lb boat ok, but where the 150 could generally hold overdrive most of the way, the Expy can not. I am extremely happy with the expy for highway cruising and it safely tows the boat, it's just abit lacking in extra power. I can lock od out and it's a completely different truck, but it would be nice to have a little extra umph to get a bit better mpg when it has to work. I didn't think the 3.31's would be that bad with the extra power in a more usable range.

 

I think the 3.31 vs the 3.55 PLUS the extra weight of the EXPY PLUS the higher gearing of the SUV are combining to cause this problem.
I see 3 different issues. The only one that can easily be improved is the RE ratio. Not sure if the gain is worth the expense.
Good luck.

 

Thanks Red. It does the job it was purchased for in any case and (as her vehicle) the wife is very happy with it. A big red bus that drives more like a mid-size car. She isn't keen on me modifying it either, unless I can do a couple small things she doesn't notice in the bank account.