Did I ruin my transmission driving in D3 and what is the difference between D3 and D4?

I was driving home today from work, a 24 mile drive, and was noticing that my RPM gauge was running high at 4500rpm while doing 70mph down the highway. At first I thought it might be my transmission going bad, then about 3 miles from home I realized I was in D3 instead of my usual D4. I didn't want to switch over while driving down the road since I thought it would drop the transmission like all the stories I have heard.

What is the difference between 2, D3, and D4? I just know to put it in D4 and drive. Did I ruin my transmission by driving in D3? The car is a 1997 honda civic with 98,500 miles.

Can my 98 Civic make a 2,400mi Road Trip?

I'm thinking of taking a road trip from Colorado to Souther California. My car is a 98 Honda Civic, 4 door. It has 115k miles on it; and the previous owners used to drive 300miles both ways every weekend or so when they took it.

I just did the oil, put new tires on, going to do the air filter soon as well. And before I decide, I'll have it checked out by a mechanic. Think it'll be fine for this drive?

My amplifier won't turn on?

I own a 2003 Honda civic, i put a sony blue tooth stereo and wired the car for sub-woofer. So when it was all said and done the amplifier didn't turn on. So i checked the current and it was getting power from the battery, and the ground was in fact grounding, but the remote didn't give any kind of signal (don't know if that means anything) and then i proceded to remove the stereo and check for current on the remote from the start (with the stereo on of course) but still got nothing from the remote. Stereo workes great with everything else, what can i be doing wrong? Amp turns on in other cars. Is the remote exit on my stereo burnt out? If so what can i do about it? Any help is welcome, thanks.

Radiator fan runs for less than a minute before turning off. Car is overheating?

I just replaced my thermostat and radiator fan sensor because my car was overheating due to the fans not turning on. Now the radiator fan does turn on but for less than a minute. It's not overheating nearly as bad as before but it has hit the red zone twice. I checked the hood to see if the fan was on and it wasn't until about 2 minutes they came back on then shut off after less than a minute while the car was still overheated.

What could be the problem. The fans are good, they blow cool air, they just don't stay on.

Honda Civic 2001

Turning on/off Honda Civic Alarm?

I have a 2009 Honda Civic coupe. I have had it for five years and never knew it had an alarm. Today while trying to get out of the car (I had to manually unlock the doors which was odd) the alarm went off when I opened the door. It hit all the buttons on the key to get it to stop, put the key in the ignition and started the car, tried pressing break and gas, nothing worked. I looked in the manual and couldn t find anything about alarm. It finally stopped, but as soon as I tried to leave again It started again.
This time, I left the door open until It stopped so I could get out of the car. It hasn't done it again since, but I d like to know how I turned it on and how to shut it off.

Do I need to get a new transmission?

I recently blew a head gasket in my 2003 Honda Civic EX and the engine got full of water. I decided to just replace the engine with a different one. I was looking at a K20A 2.0l, which is a vtec. Would I need to replace the transmission for a different one as well? If so, can I please get a list of transmissions if I do?
And if I do just get the original 1.7 vtec can you please put a link for me to the transmission so I can look at it?

Walking a away from a signed contract at the car dealership?

Ok so I went in a decided to go with a Honda Civic and then, after all the numbers were done the only car they had was a color I didn't want. So they called another dealership to transfer one. I had to go to work but before I left they said to sign the contract and it had the black car on the top not the car I wanted. The reason they made me sign the paper is to have me agree on the numbers settled. He then said I would have to sign a different contract again tomorrow. I'm going to pick up the car today but I didn't sign for that car. Does this mean I could still back out if I wanted to?

2006 Honda Civic Coupe noise?

A noise from around the left side of the engine. Mechanic says the adjuster' is bad. Have changed it twice still noise persists.