check or replace your thottle position sensor tps that trans needs to know where the throttle is to shift if it is bad it will do as you say wont shift to third
another telltale is it will act like it goes into lockup when shifting into reverse and stall the engine
If it is necessary to remove the heater assembly, the cooling system must be drained before removing the heater core.
When a heater core leaks, a new heater core is installed or the old one repaired. Heater Housing
The heater housing is usually under the dash and must be removed to gain access to the heater core.
Procedures for replacing the heater core vary with the year, make, and model of car. It threfore necessary to consult the manufacturer's repair manuals for the proper procedure for replacement.
The heater housing is disassembled to get to the heater core.
Heater Core
Remove the access panels(s) or the split heater/air conditioning case to gain acess to the heater core.
Remove the heater coolant hoses.
Remove the cable and/or vacuum control lines (if equipped).
Remove the heater core securing brackets and/or clamps.
Lift the core from the case. Do not use force. Take care not to damage the fins of the heater core when removing.
To reinstall the heater core, reverse the removal steps.
When the heater core leaks and must be repaired or replaced, it is a very difficult and time-consuming job primarily because of the core's location deep within the firewall of the car. For this reason always leak test a replacement heater core before installation.
It's possibly the amplifier. It's seperate on many of these vans. When I got a new stereo, it needed all new speaker wires just to bypass the amp. See if there is a fuse for the amp.
on this year of van there are a few problems that cause this that are common, one is the distributor stator or pickup as some call it, if the ignition system is the problem a self test of the system will reveal a fault code for the defective part, the codes u will get may be 14 and 18, u can run this test yourself with a jumper wire at the self test connector under the hood or have a dealer run the test with a scan tool called a star tester, that is the preferred way, the self test connector inside a plastic protector about the size of a flip top cigarette pack lid, it is attached by a clip to the wiring harness that runs under the hood along sealing edge of hood upper lip. here is the link to the testing procedure if u want to try and do it yourself. Watch the youtube video.
This is quite a project... I would recommend, if you're going to do this yourself, obtaining a repair manual for the van. They usually have sections to walk you through the process and go into good detail, specific for your model.
The job can be done easily in a day... get an early start though. Good luck!
i'm guessing that is premium sound... check the relay for the amplifier.. or bass booster ... can't remember what it was called on my windstar of that year but when i blew the fuse i had no sound
the quickest way to check is to start the vehicle then remove the positive battery cable, if the engine dies then the regulater in the altenator is bad and you will know that it's not charging. you will also need to check that all the connections between the battery and the vehicle are tight.. please rate this thanks
The heater housing is disassembled to get to the heater core.
Heater Core 
