Suspected Timing Belt Skip

[volvoaddict007]

Hey there,

1990 5 speed 760 Turbo Wagon 310K.
( '91 940 turbo eng. + trans.)

I've put about 55K on this car in 9 years. I believe the timing belt has about 90K miles and over 10 years old. Recently I noticed a couple times on the highway that the engine seemed to stutter one beat, perhaps a misfire.

I rolled and jump started the car recently with the 5 speed. Afterwards the car would idle usually but when given any gas it will get the RPMS up awkwardly but once it is in gear will not climb any grade at all and I can eventually get the car up to about 30 MPH on level sufaces. I changed the fuel filter. No change. I did a fuel pressure test and it is OK. When I struggled to get the car a bit uphill and out of the driveway it backfired a couple times. My mechanic who is not familiar with Volvos suspects the timing belt has skipped and I tend to agree. His diagnostic equipment only goes back to OBD II so he's reluctant to go any further.

Is there a way to confirm a timing belt skip? If it has skipped I suppose gears are marked inside the cover so that I will be able to line the new one up properly. It is past due for the belt so I might as well change it out I suppose. Any help or suggestions would be appreciated.