I have a 2004 F-150 Heritage-4.2 Auto trans-3.55 gear.I tow a 18 ft bass boat.At 70 mph rpms are 2850.I was wondering at that range on long trips is this a good thing or bad.Also at this speed getting 12 miles per gallon.What are the preferred rpms ranges for this type of set up ?

 

Did you have O/D on or off?

You shouldn't have a problem either way. Do you know what the curb weight of the boat is? Would also help if you had the curb weight of the truck? I mean curb weight as in the boat, accessories (life jackets, boat anchor, etc) and as in the truck, as people, and if anything is being hauled in the bed. Basically how much the boat and truck weight if you were take it on a trip with everything including the weight of you.

I never had a problem hauling 24' sleeper boat with small block V8 weighing in at approx. 6000 lbs according to a truck scale, with accessories, and 2 full tanks on the boat. Not to mention I had myself, my dad, my mom, and usually a friend or two. So I was pushing over 10k with my F150 that had 3.55's v6 with a 5 speed manual. NEVER had a problem. Even with all that weight, I was still able to make my LS rear axle give on a boat ramp showing I had way more than enough power.

In your case, it is nothing for the truck.

 

I run with over drive off,not sure of total weight.I was wondering if I was cranking too high on rpms. At what rpms do you run at when towing you rig. It don't have a red line is it 6 grand ?. I have never had any power related problems pulls fine.Just seems like i'm really cranking the R's

 

2850 should be fine, that engine will run at that rpm all day and all night with no harmful effects. Best efficiency when towing will be found at or around the torque peak (which is 3400 rpm with that engine), and the transmission will run cooler if the torque converter stays locked and doesn't constantly upshift and downshift. Redline is at least 5000, I've been trying to find out the exact redline but nobody can tell me. The rev limiter will kick in anyway - with an automatic it's gonna shift before that happens even under wide open throttle.

 

You should be fine Jerry, I have a '05 2wd XL with 4.2/auto 3.55's and I too tow a 18 1/2' bass boat with my O/D turned off. I usually tow mine anywhere from 70-75mph so my RPM's should be somewhat close to yours, even though I have 275/65/18 BFG's on 18" FX4 wheels, so my RPM's might be just a little lower from the added wheel diameter. I have put about 60k on my truck to date, with probably close to 15k of that towing my boat and I havent seen anything that would cause me to worry about running it at those RPM's. I'd say its easier on the motor than it would be on the the tranny if you left the O/D turned on. BTW, what kind of boat do you have? I have a '05 Skeeter with a 150 Yammie VMax