98 windstar,3.8L.acr lurches when started,you can give it gas in park and will atempt to move forward,no reverse,put in drive and you have to give alot of gas to get to move ,then it makes a horrible rattiling noise.motor is under a heavey load whole time,like holding brake while doing all this.no codes,30%load onengine in park.or any gear

SOURCE: 2003 ford windstar

Check your transmission fluid level if at all possible. If your fluid is low you won't be able to engage any gears as there isn't enough pressurized fluid to shift the clutch or selector in the transmission box. If that's fine, next check the selector link and check it is connected to the transmission (not totally unheard of for it to come loose). Still no joy then it's the clutch...sorry.

SOURCE: wont go

I would first check the transmission fluid.
if were good there then its something internal.
RD

SOURCE: Engine runs vehicle wont move Possible ring gear? 84 Topaz

Is it a metal shaft? When you put it in drive does it make any noise? Does the speedometer move? Does it make a loud clicking sound when you put it back in Park?

SOURCE: 94 F150 2-wheel drive 4-speed automatic, first

This is not good. It can be as simple as low or dirty fluid or as bad as a wornout valve body. If you know a reputable shop I would try to change the trans filter and put in new fluid.
There are some models that have a check valve under the filter so I am not advising doing it yourself.
The torque converter is your pump and it can be sluggish with dirty fluid and low rpm as you describe.
The simple maintenance may be all you need. Good Luck.

SOURCE: Driving a 2003 Ford windstar. Went to pass and

Very common on this make and model trans, pump drive splines inside torque converter strip out and pump is not turning, Most times there is no damage to pump shaft. Remove trans and remove torque converter, inspect the splines at the very bottom of the hub hole. If stripped out inspected pump shaft splines which are the smaller center splines coming out of trans, if ok replace torque converter and re-install trans, change out fluid, clean any metal from magnet and replace filter, fill with fluid and verify proper operation.