Your car has exceeded the GVW. The nose dive is a problem with your brake proportioning valve on the back wish bone. Stiff front suspention is probably seized front
struts. DO NOT use air shocks. You are using air to subsitute for the proper suspention.
Mind you you can use air shocks but you will punch out your shock towers in the trunk.
Then you have NO rear suspention as the rear bumper hits the ground. You loose 10 %
on propane mileage and power and the price of propane is more than gas. Get ride of the propane crap and go back to gas. It's much cheaper.
1: My vehicle weight on the scales at the local recycling yard shows 3235 w/ driver and 1/2 tank fuel and 80 lbs tools in trunk. Max GVW on the door sticker is 3866 lbs.
2: Brakes lock up evenly on all 4 tires in emergency stop, even w/full tank. A bad valve would show up there. The real problem is the tank sits between the wheel wells... up too high due to the so-so installation by the original owner in 1993. Tuning the suspension should compensate somewhat. The real fix would be to cut out the bottom of the trunk to remount the tank for a lower CG mounting but that's not worth all the hassles that entails it at this point. I've learned to think farther ahead when driving. A good thing for all to consider, really.
3: Front struts not seized or leaking externally. 2 people on front bumper drops it ~2" as it should. Jounce test also gives correct response.
4: I can't put air shocks on this 1992 vehicle, nor are they available. I just wish
I could for the simplicity. It's a modern STRUT suspension, not old skool coil or leaf springs and shocks (ala pre-1980). I've installed air shocks in 5 cars from that ancient time... I know the diff. There are gas charged
struts available, but I haven't got them on the Tempo. The OEM's are still in place.
5. For the last 3 years I got Propane for 10-40% less than gasoline, depending on station. In 08, I was paying $1.89 - $2.29 locally while YOU were paying 3 - 4 bucks for Arab blood money oil. At 2 stations on my 670 mile trip (each way) to Kansas 2 months ago, I paid under 2 bucks and 1 was $1.46! Trip average was $2.31/gal (Flying J demands $2.99 for motor fuel but is open 24/7). Planning your fuel stops on trips in advance is the single big disadvantage of Propane. The internet and a telephone and one day in advance are all I need. Propane is the 3rd most available fuel in America and has much lower emissions than gas or bio-diesel.
6: I never have to worry about a fuel pump, fouled plugs, oil contamination, gummy injectors, burned O2 sensors, rotted exhaust pipes, etc, etc. It occupies as only a little more space than gas per gallon, unlike Hydrogen and Methane, and doesn't require special materials or new tech to work that aren't already on the shelf. Converting back would cost $1800 for new parts anyway. I'd loose my free use of the HOV lanes and I'd be polluting the air 50% faster. Amazing that no one advertises the advantages.
Dude, you are 0-6.