I have a 2005 F150 Tritan 5.4 V8.
The transmission shutters at 40-45 mph. It doesn't do it if I have the OD Off. Any ideas to how to fix this without replacing the transmission? I see posts about changing spark plugs, could it really be that easy? Thanks

 

05 F150 with the 5.4. that might have the snappy snappy plugs but yes it could be as simple as misfires. that is usually when they first become apparent

 

I heard u have to take it in to get them replaced. They have a tendency to snap the spark plugs. I can replace them on my own, but don't want to run into this issue.

 

You don't have to. Rent/buy the lisle tool. Quite a few different methods.
How many miles on the truck?
I'd say its your plugs, not the trans.

 

I hate to disagree, but if it doesn't shudder with the O/D off, it sounds like a transmission issue. I'd do the plugs regardless, but it sounds like the symptoms when O/D dies on the tranny.

 

I see your point, but I can say from experience that for whatever weird reason.. certain misfires can be "stopped" when shutting off O/D
I remember going through that exact problem when I started creeping over 100k. Plugs were still factory. I took it to different transmission shops and they all kept saying torque converter lockup issue. Last shop I went to said to change the plugs. Did that and voila, no more shutter and shake. Why turning O/D off stopped it...I'll never know. That was over 100k miles ago and I'm still running the factory transmission. Transmission was my first thought then because it stopped when killing O/D. I almost paid for a rebuild lol

 

Agree with gone postal ...

When (if ever) was the transmission fluid changed?

HINT: Typical maintenance schedule is 30,000 - 50,000 miles
.