I'm semi new to the diesel world. I'm looking for a diesel and have narrowed my search to the 99-03 Powerstrokes.

The average price around here (Klamath Falls, Oregon) is anywhere from 13k to 20k for what I'm looking for. I don't want to spend more that 17k and have found some pretty nice trucks through autotrader.com. Here is my question;
Is it worth finding a truck with a little more miles(150k +), if it is a manual trans?
I plan to eventually run at least 35" tires, and want to upgrade the usuals like chip, exhaust, intake...
From what I've heard and researched the manual trannies cause a lot less headaches, and they can handle 850+ torque with a heavy duty clutch. Where as an automatic gives out way less stock and costs' a lot more to upgrade to handle the power.
Thank you guys for any input. It will be appreciated.
Steve