Hello and welcome to Just answer.com, Super mechanic here. About your van.
Being that the transmission was just replaced I would have to say to check the crankshaft position sensor. Sometimes when the trans is installed the CKP sensor may get damaged. You might be able to see if it is, but here is a test that you can do.
See Figures 3 and 4
Remove the engine cover.
Using the DRB-II scan tool or equivalent, plug into diagnostic connector and erase DTC's.
Turn ignition OFF and then ON again.
Crank engine until starts or for 10 seconds, whichever first. Monitor Crank Signal on scan tool. If Crank Signal is detected, CKP sensor is OK, if No Crank Signal is detected, proceed with diagnostics.
Inspect wiring and connectors and repair as necessary and retest, if wiring and connectors are OK, proceed to next step.
With the ignition OFF, unplug the CKP sensor signal. Using a voltmeter, check the supply voltage using supplied schematics.
On 1995 and earlier vehicles, it should be 7.0v or more; if not, repair circuit and retest. If voltage is OK, proceed to next step.
On 1996-98 vehicles, it should be 4.5v or more; if not, repair circuit and retest. If voltage is OK, proceed to the next step.
Using the scan tool, erase DTC's in the ECM, then turn the ignition OFFand install a jumper wire on the CKP signal circuit. Turn the ignition ON.
While observing the display on scan tool, tap the other end of the jumper wire to the sensor ground. If the scan tool shows No Cam Sync, replace the CKP sensor. If the scan tool shows a Cam Sync, proceed to next step.
With the ignition OFF, using an ohmmeter probe the ground signal on the CKP sensor connector, measure the resistance between the connector and ground. If it is less than 5.0 ohms, proceed to the next step; if it is more than 5.0v, repair the circuit and retest.
Disconnect the negative battery cable.
Disconnect the ECM wiring harness. Inspect for any damaged pins or connector terminals and repair and retest if necessary
Using an ohmmeter, test the CKP signal circuit between CKP connector and ECM connector for resistance. If it is less than 5.0 ohms, proceed to next step, if it is more than 5.0 ohms, repair the circuit and retest.
Plug in the CKP sensor connector.
Using an ohmmeter, measure the resistance between the CKP signal circuit and CKP ground at the ECM connector. If resistance is less than 5ohms, repair the short in the CKP signal wire. If the resistance is more than 5 ohms, replace the CKP sensor.