a GPS is an electronic version of your road atlas... can give u a map of the area you are in right now, down to individual streets. Not 100% accurate, no map is. I have one, the garmin nuvi 425T.. use it for trip planning, along with my atlas. Helps out at night when one can not see the street signs...or the signs are missing. Do I follow it without checking the route out first by calling ahead, NO. It is a dumb computer, use your own brain, and you will not get into trouble with one. Has helped me out when a detour was not clearly marked.. helped me see where the next road was. Night time, Oklahoma 2 lane.
From what I have read over the past year or so garmin has the best truck GPS offered in todays marketplace. The 465T is programmable to the specific size of truck you have. I recently heard an interview on satellite radio discussing Garmins newest truck oriented GPS system. It is named the DEZL. Apparently it is an upgrade over the 465T and still offers the entire NTTS breakdown directory. According to the website the 560 LMT also offers free lifetime map upgrades. The system has not made it into stores yet but it may be worth keeping an eye on.
My garmin has no troubles recognizing toll roads..all in the options you set. And if you have it set to avoid highways, then yes it will route you around and around. Also has a faster route or shorter route option...Have had mine for 3 years now. Also have the lifetime map updates, and the quarterly updates. Very quick calculations too. Has NEVER routed me onto a road I should not be on, or to a bridge that was too low... Now I have argued with it, and took my own route, without due diligence, and been in a few embarrassing spots. Learned from my mistakes, and now double check my routes.
You can program it to a specific truck size but, that means nothing if the GPS unit don't have the correct bridge height.
If your gonna get a gps make sure it is trucker friendly, Most of the ones they sell at truck stops are made just for trucks, And agreed with everything scottied has said,But definately compare directions you get with the ones the company gives you. gps is great for averaging out things as well use all available resources you can get.
So far I have not had a single bridge be lower than the 465T though. Although sometimes the 465T lists them lower than they really are.
One time my GPS led me to a place called "Donna's Ranch" in Wells Nevada! BOY! was my wife mad when she woke up in the truck and found it parked there!
I have a pc miler 450 truck gps. I picked it because it has great reviews on a certain website and it is listed as best for Canada when it comes to truck specific versions. Prior to that I had a garmin nuvi 255w which is not truck specific. I should have kept the garmin but wanted a new toy and figured since the garmin was a few years old -ancient in technology life cycles- and not truck specific the new one could only be better. Like mentioned by almost everyone the gps is just another tool in the box. It is excellent for eta's. It's excellent for knowing where you are and how far it is before that street you have to turn down. It has many pluses but no matter how accurate it is with truck routing and how up to date the maps are you can't rely on it being correct. Because of that my recommendation is a regular garmin. I can't speak about the tnd but the garmin is better than the pcm for user friendliness and for address accuracy. I don't think the truck ones have reached the point that they are worth the extra money.